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

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

Index: third_party/WebKit/Source/core/layout/compositing/GraphicsLayerUpdater.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/GraphicsLayerUpdater.cpp b/third_party/WebKit/Source/core/layout/compositing/GraphicsLayerUpdater.cpp
index ccec84d0159bc2911b6e9e14816ae9aff9a11378..0f6a32830c79abea2716b4809dc486ada39a8e73 100644
--- a/third_party/WebKit/Source/core/layout/compositing/GraphicsLayerUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/GraphicsLayerUpdater.cpp
@@ -28,6 +28,7 @@
 
 #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"
@@ -53,6 +54,10 @@ class GraphicsLayerUpdater::UpdateContext {
   }
 
   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;
   }