Ensure unique LayerIds for pseudo-elements

Currently pseudo-elements, like the fragments created for ::before and
::after, with layers will have the same LayerId as the body of their
owning fragments. Instead all LayerIds should be unique.

Fixes #2010.

1 files changed, 10 insertions, 3 deletions

diff --git a/components/layout/flow.rs b/components/layout/flow.rs
index 51321e75b2c..578a95fb05c 100644
--- a/components/layout/flow.rs
+++ b/components/layout/flow.rs
@@ -48,7 +48,7 @@ use wrapper::{PseudoElementType, ThreadSafeLayoutNode};
 
 use euclid::{Point2D, Rect, Size2D};
 use gfx::display_list::ClippingRegion;
-use msg::compositor_msg::LayerId;
+use msg::compositor_msg::{LayerId, LayerType};
 use msg::constellation_msg::ConstellationChan;
 use rustc_serialize::{Encoder, Encodable};
 use std::fmt;
@@ -359,9 +359,16 @@ pub trait Flow: fmt::Debug + Sync + Send + 'static {
 
     /// Returns a layer ID for the given fragment.
     #[allow(unsafe_code)]
-    fn layer_id(&self, fragment_id: u32) -> LayerId {
+    fn layer_id(&self) -> LayerId {
         let obj = unsafe { mem::transmute::<&&Self, &raw::TraitObject>(&self) };
-        LayerId(obj.data as usize, fragment_id, 0)
+        LayerId::new_of_type(LayerType::FragmentBody, obj.data as usize)
+    }
+
+    /// Returns a layer ID for the given fragment.
+    #[allow(unsafe_code)]
+    fn layer_id_for_overflow_scroll(&self) -> LayerId {
+        let obj = unsafe { mem::transmute::<&&Self, &raw::TraitObject>(&self) };
+        LayerId::new_of_type(LayerType::OverflowScroll, obj.data as usize)
     }
 
     /// Attempts to perform incremental fixup of this flow by replacing its fragment's style with