Avoid to resolve CMAA for read and draw without content changed or with content committed.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
index 909e548229317c4bcb33c808427e72162135df73..21000f7f4e2158b3e42e07a5538799bcf9dd958a 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -968,7 +968,7 @@ bool DrawingBuffer::resizeFramebufferInternal(const IntSize& newSize) {
 }
 
 void DrawingBuffer::resolveAndBindForReadAndDraw() {
-  {
+  if (m_contentsChanged) {

[dshwang, 2017/04/08 02:16:32]

I think it's better to change
m_antiAliasingMode != None && !m_contentsChangeResolved
in DrawingBuffer::resolveIfNeeded().
What do you think?

[Zhenyao Mo, 2017/04/12 23:38:08]

I agree !m_contentsChangeResolved is a better condition.  However, this is
already a condition in resolveMultisampleFramebufferInternal() which is called
by resolveIfNeeded().  So why do we want to repeat it here? (Maybe I missed
something?)

[xinghua.cao, 2017/04/13 10:50:24]

It seems a repeating condition here, thank you.

     ScopedStateRestorer scopedStateRestorer(this);
     resolveIfNeeded();
   }
@@ -1006,7 +1006,8 @@ void DrawingBuffer::resolveMultisampleFramebufferInternal() {
   }
 
   m_gl->BindFramebuffer(GL_FRAMEBUFFER, m_fbo);
-  if (m_antiAliasingMode == ScreenSpaceAntialiasing)
+  if (m_antiAliasingMode == ScreenSpaceAntialiasing &&
+      !m_contentsChangeResolved)
     m_gl->ApplyScreenSpaceAntialiasingCHROMIUM();
 }