Skip paint chunks with effectively invisible opacity.

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

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 548 matching lines @@
 
   // Adjusts the given rect (in the coordinate space of the LayoutObject) to the
   // coordinate space of |paintInvalidationContainer|'s GraphicsLayer backing.
   // Should use PaintInvalidationState::mapRectToPaintInvalidationBacking()
   // instead if PaintInvalidationState is available.
   static void MapRectToPaintInvalidationBacking(
       const LayoutObject&,
       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.
   ScrollingCoordinator* GetScrollingCoordinator();
 
   // Returns true if the element or any ancestor is transformed.
   bool CompositesWithTransform() const;
 
   // Returns true if the element or any ancestor has non 1 opacity.
   bool CompositesWithOpacity() const;
@@ skipping 432 matching lines @@
   void ClearSelfPaintingStatusChanged() {
     DCHECK(!RuntimeEnabledFeatures::slimmingPaintV2Enabled());
     self_painting_status_changed_ = false;
   }
 
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
   void EndShouldKeepAliveAllClientsRecursive();
 #endif
 
  private:
+  bool IsComposited() const;
+
   void SetNeedsCompositingInputsUpdateInternal();
 
   void Update3DTransformedDescendantStatus();
 
   // Bounding box in the coordinates of this layer.
   LayoutRect LogicalBoundingBox() const;
 
   bool HasOverflowControls() const;
 
   void DirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
@@ skipping 241 matching lines @@
 
 }  // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 CORE_EXPORT void showLayerTree(const blink::PaintLayer*);
 CORE_EXPORT void showLayerTree(const blink::LayoutObject*);
 #endif
 
 #endif  // Layer_h