Auto merge of #21931 - jdm:reload-images, r=emilio

Make layout use available image data before querying the image cache.

These changes make layout more efficient for any page which contains images that have already loaded, since it does not require synchronously querying the image cache thread for each image present. It also makes reloading a page actually display the images that are already in the image cache.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #21919
- [x] There are tests for these changes

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5 files changed, 58 insertions, 5 deletions

diff --git a/components/layout/fragment.rs b/components/layout/fragment.rs
index 33a6ac3dd3b..486a344989b 100644
--- a/components/layout/fragment.rs
+++ b/components/layout/fragment.rs
@@ -401,6 +401,11 @@ pub struct ImageFragmentInfo {
     pub metadata: Option<ImageMetadata>,
 }
 
+enum ImageOrMetadata {
+    Image(Arc<Image>),
+    Metadata(ImageMetadata),
+}
+
 impl ImageFragmentInfo {
     /// Creates a new image fragment from the given URL and local image cache.
     ///
@@ -412,14 +417,29 @@ impl ImageFragmentInfo {
         node: &N,
         layout_context: &LayoutContext,
     ) -> ImageFragmentInfo {
-        let image_or_metadata = url.and_then(|url| {
-            layout_context.get_or_request_image_or_meta(node.opaque(), url, UsePlaceholder::Yes)
-        });
+        // First use any image data present in the element...
+        let image_or_metadata = node.image_data().and_then(|(image, metadata)| {
+            match (image, metadata) {
+                (Some(image), _) => Some(ImageOrMetadata::Image(image)),
+                (None, Some(metadata)) => Some(ImageOrMetadata::Metadata(metadata)),
+                _ => None,
+            }
+        }).or_else(|| url.and_then(|url| {
+            // Otherwise query the image cache for anything known about the associated source URL.
+            layout_context.get_or_request_image_or_meta(
+                node.opaque(),
+                url,
+                UsePlaceholder::Yes
+            ).map(|result| match result {
+                ImageOrMetadataAvailable::ImageAvailable(i, _) => ImageOrMetadata::Image(i),
+                ImageOrMetadataAvailable::MetadataAvailable(m) => ImageOrMetadata::Metadata(m),
+            })
+        }));
 
         let current_pixel_density = density.unwrap_or(1f64);
 
         let (image, metadata) = match image_or_metadata {
-            Some(ImageOrMetadataAvailable::ImageAvailable(i, _)) => {
+            Some(ImageOrMetadata::Image(i)) => {
                 let height = (i.height as f64 / current_pixel_density) as u32;
                 let width = (i.width as f64 / current_pixel_density) as u32;
                 (
@@ -434,7 +454,7 @@ impl ImageFragmentInfo {
                     }),
                 )
             },
-            Some(ImageOrMetadataAvailable::MetadataAvailable(m)) => {
+            Some(ImageOrMetadata::Metadata(m)) => {
                 (
                     None,
                     Some(ImageMetadata {
diff --git a/components/layout_thread/dom_wrapper.rs b/components/layout_thread/dom_wrapper.rs
index 3c3495ee6fe..bd760204884 100644
--- a/components/layout_thread/dom_wrapper.rs
+++ b/components/layout_thread/dom_wrapper.rs
@@ -36,6 +36,7 @@ use html5ever::{LocalName, Namespace};
 use layout::data::StyleAndLayoutData;
 use layout::wrapper::GetRawData;
 use msg::constellation_msg::{BrowsingContextId, PipelineId};
+use net_traits::image::base::{Image, ImageMetadata};
 use range::Range;
 use script::layout_exports::{CharacterDataTypeId, ElementTypeId, HTMLElementTypeId, NodeTypeId};
 use script::layout_exports::{Document, Element, Node, Text};
@@ -59,6 +60,7 @@ use std::fmt::Debug;
 use std::hash::{Hash, Hasher};
 use std::marker::PhantomData;
 use std::ptr::NonNull;
+use std::sync::Arc as StdArc;
 use std::sync::atomic::Ordering;
 use style::CaseSensitivityExt;
 use style::applicable_declarations::ApplicableDeclarationBlock;
@@ -1048,6 +1050,11 @@ impl<'ln> ThreadSafeLayoutNode for ServoThreadSafeLayoutNode<'ln> {
         this.image_density()
     }
 
+    fn image_data(&self) -> Option<(Option<StdArc<Image>>, Option<ImageMetadata>)> {
+        let this = unsafe { self.get_jsmanaged() };
+        this.image_data()
+    }
+
     fn canvas_data(&self) -> Option<HTMLCanvasData> {
         let this = unsafe { self.get_jsmanaged() };
         this.canvas_data()
diff --git a/components/script/dom/htmlimageelement.rs b/components/script/dom/htmlimageelement.rs
index ca9243beb1b..b31c5e886af 100644
--- a/components/script/dom/htmlimageelement.rs
+++ b/components/script/dom/htmlimageelement.rs
@@ -1328,6 +1328,9 @@ pub trait LayoutHTMLImageElementHelpers {
     #[allow(unsafe_code)]
     unsafe fn image_density(&self) -> Option<f64>;
 
+    #[allow(unsafe_code)]
+    unsafe fn image_data(&self) -> (Option<Arc<Image>>, Option<ImageMetadata>);
+
     fn get_width(&self) -> LengthOrPercentageOrAuto;
     fn get_height(&self) -> LengthOrPercentageOrAuto;
 }
@@ -1352,6 +1355,14 @@ impl LayoutHTMLImageElementHelpers for LayoutDom<HTMLImageElement> {
     }
 
     #[allow(unsafe_code)]
+    unsafe fn image_data(&self) -> (Option<Arc<Image>>, Option<ImageMetadata>) {
+        let current_request = (*self.unsafe_get())
+            .current_request
+            .borrow_for_layout();
+        (current_request.image.clone(), current_request.metadata.clone())
+    }
+
+    #[allow(unsafe_code)]
     unsafe fn image_density(&self) -> Option<f64> {
         (*self.unsafe_get())
             .current_request
diff --git a/components/script/dom/node.rs b/components/script/dom/node.rs
index 1a5a23f4ef6..8024f2a04a7 100644
--- a/components/script/dom/node.rs
+++ b/components/script/dom/node.rs
@@ -62,6 +62,7 @@ use js::jsapi::{JSContext, JSObject, JSRuntime};
 use libc::{self, c_void, uintptr_t};
 use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
 use msg::constellation_msg::{BrowsingContextId, PipelineId};
+use net_traits::image::base::{Image, ImageMetadata};
 use ref_slice::ref_slice;
 use script_layout_interface::{HTMLCanvasData, HTMLMediaData, LayoutElementType, LayoutNodeType};
 use script_layout_interface::{OpaqueStyleAndLayoutData, SVGSVGData, TrustedNodeAddress};
@@ -81,6 +82,7 @@ use std::default::Default;
 use std::iter;
 use std::mem;
 use std::ops::Range;
+use std::sync::Arc as StdArc;
 use style::context::QuirksMode;
 use style::dom::OpaqueNode;
 use style::selector_parser::{SelectorImpl, SelectorParser};
@@ -1086,6 +1088,7 @@ pub trait LayoutNodeHelpers {
     fn selection(&self) -> Option<Range<usize>>;
     fn image_url(&self) -> Option<ServoUrl>;
     fn image_density(&self) -> Option<f64>;
+    fn image_data(&self) -> Option<(Option<StdArc<Image>>, Option<ImageMetadata>)>;
     fn canvas_data(&self) -> Option<HTMLCanvasData>;
     fn media_data(&self) -> Option<HTMLMediaData>;
     fn svg_data(&self) -> Option<SVGSVGData>;
@@ -1234,6 +1237,13 @@ impl LayoutNodeHelpers for LayoutDom<Node> {
     }
 
     #[allow(unsafe_code)]
+    fn image_data(&self) -> Option<(Option<StdArc<Image>>, Option<ImageMetadata>)> {
+        unsafe {
+            self.downcast::<HTMLImageElement>().map(|e| e.image_data())
+        }
+    }
+
+    #[allow(unsafe_code)]
     fn image_density(&self) -> Option<f64> {
         unsafe {
             self.downcast::<HTMLImageElement>()
diff --git a/components/script_layout_interface/wrapper_traits.rs b/components/script_layout_interface/wrapper_traits.rs
index 9df6a7b44f4..6bce47ec845 100644
--- a/components/script_layout_interface/wrapper_traits.rs
+++ b/components/script_layout_interface/wrapper_traits.rs
@@ -13,10 +13,12 @@ use atomic_refcell::AtomicRef;
 use gfx_traits::{ByteIndex, FragmentType, combine_id_with_fragment_type};
 use html5ever::{Namespace, LocalName};
 use msg::constellation_msg::{BrowsingContextId, PipelineId};
+use net_traits::image::base::{Image, ImageMetadata};
 use range::Range;
 use servo_arc::Arc;
 use servo_url::ServoUrl;
 use std::fmt::Debug;
+use std::sync::Arc as StdArc;
 use style::attr::AttrValue;
 use style::context::SharedStyleContext;
 use style::data::ElementData;
@@ -276,6 +278,9 @@ pub trait ThreadSafeLayoutNode:
     /// If this is an image element, returns its current-pixel-density. If this is not an image element, fails.
     fn image_density(&self) -> Option<f64>;
 
+    /// If this is an image element, returns its image data. Otherwise, returns `None`.
+    fn image_data(&self) -> Option<(Option<StdArc<Image>>, Option<ImageMetadata>)>;
+
     fn canvas_data(&self) -> Option<HTMLCanvasData>;
 
     fn svg_data(&self) -> Option<SVGSVGData>;