Fix shouldPaint issue when a composited floating iframe becomes non-self-painting

third_party/WebKit/Source/core/paint/BlockFlowPainter.cpp

Index: third_party/WebKit/Source/core/paint/BlockFlowPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/BlockFlowPainter.cpp b/third_party/WebKit/Source/core/paint/BlockFlowPainter.cpp
index 816eaf5cf43ecdd038a9061c3c231b07cc450d9c..0ac6dd659b642bb3bd07362ed8ae7be405ee7e22 100644
--- a/third_party/WebKit/Source/core/paint/BlockFlowPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/BlockFlowPainter.cpp
@@ -53,6 +53,10 @@ void BlockFlowPainter::paintFloats(const PaintInfo& paintInfo,
       continue;
 
     const LayoutBox* floatingLayoutObject = floatingObject->layoutObject();
+    // TODO(wangxianzhu): Should this be a DCHECK?
+    if (floatingLayoutObject->hasSelfPaintingLayer())

[chrishtr, 2017/01/25 20:47:57]

In my original patch, I removed this because it was impossible to trigger for
non-self-painting layers. Why would it trigger now?

[Xianzhu, 2017/01/25 21:03:25]

I didn't look at this closely when applying the revert. This CL needs to be
merged into M56, so I would like to take the safe side.

+      continue;
+
     // FIXME: LayoutPoint version of xPositionForFloatIncludingMargin would make
     // this much cleaner.
     LayoutPoint childPoint = m_layoutBlockFlow.flipFloatForWritingModeForChild(