Clarify GraphicsContext::beginLayer()/endLayer() have unexpected behaviors.

Source/platform/graphics/GraphicsContext.cpp

 /*
  * Copyright (C) 2003, 2004, 2005, 2006, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2013 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 173 matching lines @@
     }
 }
 
 void GraphicsContext::saveLayer(const SkRect* bounds, const SkPaint* paint)
 {
     if (contextDisabled())
         return;
 
     ASSERT(m_canvas);
 
-    realizeCanvasSave();
-
+    m_paintState->incrementSaveCount();
+    m_canvasStateStack.append(CanvasSaveState(m_pendingCanvasSave, m_canvas->getSaveCount()));
     m_canvas->saveLayer(bounds, paint);
+    m_pendingCanvasSave = false;
     if (regionTrackingEnabled())
         m_trackedRegion.pushCanvasLayer(paint);
 }
 
 void GraphicsContext::restoreLayer()
 {
     if (contextDisabled())
         return;
 
     ASSERT(m_canvas);
 
-    m_canvas->restore();
+    restore();
     if (regionTrackingEnabled())
         m_trackedRegion.popCanvasLayer(this);
 }
 
 void GraphicsContext::beginAnnotation(const AnnotationList& annotations)
 {
     if (contextDisabled())
         return;
 
     ASSERT(m_canvas);
@@ skipping 1794 matching lines @@
         // FIXME: This is to not break tests (it results in the filter bitmap flag
         // being set to true). We need to decide if we respect InterpolationNone
         // being returned from computeInterpolationQuality.
         resampling = InterpolationLow;
     }
     resampling = limitInterpolationQuality(this, resampling);
     paint->setFilterLevel(static_cast<SkPaint::FilterLevel>(resampling));
 }
 
 } // namespace blink