Adjust DrawingBuffer's visibility tracking behavior with lost context

Source/platform/graphics/gpu/DrawingBuffer.cpp

 /*
  * Copyright (c) 2010, 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 190 matching lines @@
 void DrawingBuffer::freeRecycledMailboxes()
 {
     if (m_recycledMailboxQueue.isEmpty())
         return;
     while (!m_recycledMailboxQueue.isEmpty())
         deleteMailbox(m_recycledMailboxQueue.takeLast());
 }
 
 bool DrawingBuffer::prepareMailbox(WebExternalTextureMailbox* outMailbox, WebExternalBitmap* bitmap)
 {
-    ASSERT(!m_isHidden);
-    if (!m_contentsChanged)
-        return false;
-
     if (m_destructionInProgress) {
         // It can be hit in the following sequence.
         // 1. WebGL draws something.
         // 2. The compositor begins the frame.
         // 3. Javascript makes a context lost using WEBGL_lose_context extension.
         // 4. Here.
         return false;
     }
+    ASSERT(!m_isHidden);
+    if (!m_contentsChanged)
+        return false;
 
     // Resolve the multisampled buffer into m_colorBuffer texture.
     if (m_multisampleMode != None)
         commit();
 
     if (bitmap) {
         bitmap->setSize(size());
 
         unsigned char* pixels = bitmap->pixels();
         bool needPremultiply = m_actualAttributes.alpha && !m_actualAttributes.premultipliedAlpha;
@@ skipping 814 matching lines @@
 void DrawingBuffer::deleteChromiumImageForTexture(TextureInfo* info)
 {
     if (info->imageId) {
         m_context->releaseTexImage2DCHROMIUM(GL_TEXTURE_2D, info->imageId);
         m_context->destroyImageCHROMIUM(info->imageId);
         info->imageId = 0;
     }
 }
 
 } // namespace blink