When setting needsRepaint, don't stop at non-stacking composited PaintLayers.

third_party/WebKit/Source/core/layout/compositing/GraphicsLayerUpdater.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 10 matching lines @@
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "core/layout/compositing/GraphicsLayerUpdater.h"
 
 #include "core/html/HTMLMediaElement.h"
 #include "core/inspector/InspectorTraceEvents.h"
+#include "core/layout/LayoutBlock.h"
 #include "core/layout/compositing/CompositedLayerMapping.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/paint/PaintLayer.h"
 #include "platform/instrumentation/tracing/TraceEvent.h"
 
 namespace blink {
 
 class GraphicsLayerUpdater::UpdateContext {
  public:
   UpdateContext()
       : m_compositingStackingContext(nullptr), m_compositingAncestor(nullptr) {}
 
   UpdateContext(const UpdateContext& other, const PaintLayer& layer)
       : m_compositingStackingContext(other.m_compositingStackingContext),
         m_compositingAncestor(other.compositingContainer(layer)) {
     CompositingState compositingState = layer.compositingState();
     if (compositingState != NotComposited &&
         compositingState != PaintsIntoGroupedBacking) {
       m_compositingAncestor = &layer;
       if (layer.stackingNode()->isStackingContext())
         m_compositingStackingContext = &layer;
     }
   }
 
   const PaintLayer* compositingContainer(const PaintLayer& layer) const {
+    // TODO(chrishtr) this is not very performant for floats, but they should
+    // be uncommon enough, and SPv2 will remove this code.
+    if (layer.layoutObject()->isFloating())
+      return layer.layoutObject()->containingBlock()->enclosingLayer();

[Xianzhu, 2017/01/09 20:04:14]

Two comments:

1. For performance we can use
   if (layer.layoutObject()->isFloating() &&
!layer.layoutObject()->parent()->isLayoutBlockFlow())
to make the slow line 60 apply to the rare case only.
(This 

2. Should we put the above logic where we set m_compositingAncestor?

[chrishtr, 2017/01/09 23:28:33]

Done.
 
That seems tricky, because it differs based on descendants being floats
and this item being not a block.

     return layer.stackingNode()->isStacked() ? m_compositingStackingContext
                                              : m_compositingAncestor;
   }
 
   const PaintLayer* compositingStackingContext() const {
     return m_compositingStackingContext;
   }
 
  private:
   const PaintLayer* m_compositingStackingContext;
@@ skipping 56 matching lines @@
         ->assertNeedsToUpdateGraphicsLayerBitsCleared();
 
   for (PaintLayer* child = layer.firstChild(); child;
        child = child->nextSibling())
     assertNeedsToUpdateGraphicsLayerBitsCleared(*child);
 }
 
 #endif
 
 }  // namespace blink