Auto merge of #11890 - shinglyu:viewport-percent-recalc, r=mbrubeck

Bug 10104 - Only restyle nodes that uses viewport percentage units on viewport size change

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Bug 10104 - Only restyle nodes that uses viewport percentage units on viewport size change
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #10104 (github issue number if applicable).

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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2 files changed, 21 insertions, 2 deletions

diff --git a/components/script/dom/node.rs b/components/script/dom/node.rs
index 5cb2ac540c4..37495be3ba3 100644
--- a/components/script/dom/node.rs
+++ b/components/script/dom/node.rs
@@ -159,7 +159,9 @@ bitflags! {
         const SEQUENTIALLY_FOCUSABLE = 0x20,
 
         /// Whether any ancestor is a fragmentation container
-        const CAN_BE_FRAGMENTED = 0x40
+        const CAN_BE_FRAGMENTED = 0x40,
+        #[doc = "Specifies whether this node needs to be dirted when viewport size changed."]
+        const DIRTY_ON_VIEWPORT_SIZE_CHANGE = 0x80
     }
 }
 
diff --git a/components/script/layout_wrapper.rs b/components/script/layout_wrapper.rs
index ebc2da9c529..78a6b1a2f71 100644
--- a/components/script/layout_wrapper.rs
+++ b/components/script/layout_wrapper.rs
@@ -36,7 +36,7 @@ use dom::bindings::js::LayoutJS;
 use dom::characterdata::LayoutCharacterDataHelpers;
 use dom::document::{Document, LayoutDocumentHelpers};
 use dom::element::{Element, LayoutElementHelpers, RawLayoutElementHelpers};
-use dom::node::{CAN_BE_FRAGMENTED, HAS_CHANGED, HAS_DIRTY_DESCENDANTS, IS_DIRTY};
+use dom::node::{CAN_BE_FRAGMENTED, HAS_CHANGED, HAS_DIRTY_DESCENDANTS, IS_DIRTY, DIRTY_ON_VIEWPORT_SIZE_CHANGE};
 use dom::node::{Node, LayoutNodeHelpers};
 use dom::text::Text;
 use gfx_traits::ByteIndex;
@@ -193,6 +193,23 @@ impl<'ln> TNode for ServoLayoutNode<'ln> {
         self.node.set_flag(HAS_DIRTY_DESCENDANTS, value)
     }
 
+    fn needs_dirty_on_viewport_size_changed(&self) -> bool {
+        unsafe { self.node.get_flag(DIRTY_ON_VIEWPORT_SIZE_CHANGE) }
+    }
+
+    unsafe fn set_dirty_on_viewport_size_changed(&self) {
+        self.node.set_flag(DIRTY_ON_VIEWPORT_SIZE_CHANGE, true);
+    }
+
+    fn set_descendants_dirty_on_viewport_size_changed(&self) {
+        for ref child in self.children() {
+            unsafe {
+                child.set_dirty_on_viewport_size_changed();
+            }
+            child.set_descendants_dirty_on_viewport_size_changed();
+        }
+    }
+
     fn can_be_fragmented(&self) -> bool {
         unsafe { self.node.get_flag(CAN_BE_FRAGMENTED) }
     }