Turn off computation of the interest rect in cc in synchronized paint mode.

third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp

Index: third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp b/third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp
index 258e0dd92f759b1febf47fb6a1913a3da1129c2b..ebe11a6cf8af823296636b89fd90571c827ff52b 100644
--- a/third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp
@@ -292,6 +292,13 @@ void GraphicsLayer::setOffsetDoubleFromLayoutObject(const DoubleSize& offset, Sh
         setNeedsDisplay();
 }
 
+IntRect GraphicsLayer::interestRect()
+{
+    if (!RuntimeEnabledFeatures::slimmingPaintSynchronizedPaintingEnabled())
+        m_previousInterestRect = m_client->computeInterestRect(this, m_previousInterestRect);
+    return m_previousInterestRect;
+}
+
 void GraphicsLayer::paint(GraphicsContext& context, const IntRect* interestRect)
 {
     ASSERT(interestRect || RuntimeEnabledFeatures::slimmingPaintSynchronizedPaintingEnabled());
@@ -324,9 +331,9 @@ void GraphicsLayer::paint(GraphicsContext& context, const IntRect* interestRect)
         }
     }
 
+    m_previousInterestRect = *interestRect;
     m_client->paintContents(this, context, m_paintingPhase, *interestRect);
     notifyFirstPaintToClient();
-    m_previousInterestRect = *interestRect;
 }
 
 void GraphicsLayer::notifyFirstPaintToClient()