WebGL: Don't destroy mailbox textures in the destructor until they're released.

Source/core/html/canvas/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 703 matching lines @@
 
     if (!m_drawingBuffer)
         return;
 
     m_extensionsUtil.clear();
 
     webContext()->setContextLostCallback(0);
     webContext()->setErrorMessageCallback(0);
 
     ASSERT(m_drawingBuffer);
+    m_drawingBuffer->beginDestruction();
     m_drawingBuffer.clear();
 }
 
 void WebGLRenderingContextBase::markContextChanged(ContentChangeType changeType)
 {
     if (m_framebufferBinding || isContextLost())
         return;
 
     m_drawingBuffer->markContentsChanged();
 
@@ skipping 4698 matching lines @@
     LocalFrame* frame = canvas()->document().frame();
     if (!frame)
         return;
 
     Settings* settings = frame->settings();
 
     if (!frame->loader().client()->allowWebGL(settings && settings->webGLEnabled()))
         return;
 
     // If the context was lost due to RealLostContext, we need to destroy the old DrawingBuffer before creating new DrawingBuffer to ensure resource budget enough.
-    m_drawingBuffer.clear();
+    if (m_drawingBuffer) {
+        m_drawingBuffer->beginDestruction();
+        m_drawingBuffer.clear();
+    }
 
     blink::WebGraphicsContext3D::Attributes attributes = m_requestedAttributes->attributes(canvas()->document().topDocument().url().string(), settings);
     OwnPtr<blink::WebGraphicsContext3D> context = adoptPtr(blink::Platform::current()->createOffscreenGraphicsContext3D(attributes, 0));
     RefPtr<DrawingBuffer> drawingBuffer;
     if (context) {
         RefPtr<WebGLRenderingContextEvictionManager> contextEvictionManager = adoptRef(new WebGLRenderingContextEvictionManager());
 
         // Construct a new drawing buffer with the new WebGraphicsContext3D.
         DrawingBuffer::PreserveDrawingBuffer preserve = m_requestedAttributes->preserveDrawingBuffer() ? DrawingBuffer::Preserve : DrawingBuffer::Discard;
         drawingBuffer = DrawingBuffer::create(context.release(), clampedCanvasSize(), preserve, contextEvictionManager.release());
@@ skipping 207 matching lines @@
         if (m_textureUnits[i].m_texture2DBinding
             || m_textureUnits[i].m_textureCubeMapBinding) {
             m_onePlusMaxNonDefaultTextureUnit = i + 1;
             return;
         }
     }
     m_onePlusMaxNonDefaultTextureUnit = 0;
 }
 
 } // namespace WebCore