Skip paint chunks with effectively invisible opacity.

third_party/WebKit/Source/core/paint/PaintLayer.h

Index: third_party/WebKit/Source/core/paint/PaintLayer.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.h b/third_party/WebKit/Source/core/paint/PaintLayer.h
index 83691b8b2a5b1467e59f4bee882dd28c06d63e57..25901a39748c4d1e958b5ee43c8cab0d4d4702c4 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -566,11 +566,7 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
       const LayoutBoxModelObject& paint_invalidation_container,
       LayoutRect&);
 
-  bool PaintsWithTransparency(GlobalPaintFlags global_paint_flags) const {
-    return IsTransparent() &&

[wkorman, 2017/04/24 19:49:37]

After this change nothing seems to use the kPaintLayerHaveTransparency flag in
PaintLayerFlags. We set it but never subsequently test it. Should we remove it
in separate change? We might even be able to delete PaintsWithTransparency or at
least centralize logic a bit, these two need to be reviewed:

[1]
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/paint/Pai...

[2]
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/paint/Pai...

-           ((global_paint_flags & kGlobalPaintFlattenCompositingLayers) ||
-            GetCompositingState() != kPaintsIntoOwnBacking);
-  }
+  bool PaintsWithTransparency(GlobalPaintFlags) const;
 
   // Returns the ScrollingCoordinator associated with this layer, if
   // any. Otherwise nullptr.
@@ -1023,6 +1019,8 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
 #endif
 
  private:
+  bool IsComposited() const;
+
   void SetNeedsCompositingInputsUpdateInternal();
 
   void Update3DTransformedDescendantStatus();