Reduce the number of layers

- overflow elements triggered all layers before them to be composited;
  this is not needed at all...
- fixed elements will trigger layers after them to be composited, but
  we don't need to composite all of them -- the one fully contained
  into previous composited layers don't need to...

bug:5069090

Change-Id: I65f789f490b837a16096b4cb186c45ade1605b41

1 files changed, 8 insertions, 1 deletions

diff --git a/Source/WebCore/rendering/RenderLayer.h b/Source/WebCore/rendering/RenderLayer.h
index 2174920..f257593 100644
--- a/Source/WebCore/rendering/RenderLayer.h
+++ b/Source/WebCore/rendering/RenderLayer.h
@@ -354,7 +354,7 @@ public:
       if (hasOverflowScroll())
           return true;
 #endif
-      return !hasAutoZIndex() || renderer()->isRenderView() || (isComposited() && isFixed());
+      return !hasAutoZIndex() || renderer()->isRenderView() || (isComposited() && isFixed()) || m_shouldComposite;
     }
 #else
 #if ENABLE(ANDROID_OVERFLOW_SCROLL)
@@ -641,6 +641,10 @@ private:
     
     bool mustOverlapCompositedLayers() const { return m_mustOverlapCompositedLayers; }
     void setMustOverlapCompositedLayers(bool b) { m_mustOverlapCompositedLayers = b; }
+#if ENABLE(COMPOSITED_FIXED_ELEMENTS)
+    bool shouldComposite() { return m_shouldComposite; }
+    void setShouldComposite(bool b) { m_shouldComposite = b; }
+#endif
 #endif
 
     void updateContentsScale(float);
@@ -743,6 +747,9 @@ protected:
 #if USE(ACCELERATED_COMPOSITING)
     bool m_hasCompositingDescendant : 1; // In the z-order tree.
     bool m_mustOverlapCompositedLayers : 1;
+#if ENABLE(COMPOSITED_FIXED_ELEMENTS)
+    bool m_shouldComposite : 1;
+#endif
 #endif
 
     bool m_containsDirtyOverlayScrollbars : 1;