WebVR: clear screen after submit if preserveDrawingBuffer is false.

third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1499 matching lines @@
   // Call the DrawingBufferClient method to restore scissor test, mask, and
   // clear values, because we dirtied them above.
   DrawingBufferClientRestoreScissorTest();
   DrawingBufferClientRestoreMaskAndClearValues();
 
   drawingBuffer()->setBufferClearNeeded(false);
 
   return combinedClear ? CombinedClear : JustClear;
 }
 
+void WebGLRenderingContextBase::markCompositedAndClearBackbufferIfNeeded() {
+  markLayerComposited();
+  clearIfComposited();
+}
+
 void WebGLRenderingContextBase::restoreScissorEnabled() {
   if (isContextLost())
     return;
 
   if (m_scissorEnabled) {
     contextGL()->Enable(GL_SCISSOR_TEST);
   } else {
     contextGL()->Disable(GL_SCISSOR_TEST);
   }
 }
@@ skipping 6310 matching lines @@
 
 void WebGLRenderingContextBase::getHTMLOrOffscreenCanvas(
     HTMLCanvasElementOrOffscreenCanvas& result) const {
   if (canvas())
     result.setHTMLCanvasElement(canvas());
   else
     result.setOffscreenCanvas(offscreenCanvas());
 }
 
 }  // namespace blink