Fix imageSourceURL() for WebGL elements.

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 411 matching lines @@
     }
     if (m_requestedAttributes.stencil) {
         blink::WGC3Dint stencilBits = 0;
         m_context->getIntegerv(GL_STENCIL_BITS, &stencilBits);
         m_actualAttributes.stencil = stencilBits > 0;
     }
     m_actualAttributes.antialias = multisample();
     return true;
 }
 
-bool DrawingBuffer::copyToPlatformTexture(blink::WebGraphicsContext3D* context, Platform3DObject texture, GLenum internalFormat, GLenum destType, GLint level, bool premultiplyAlpha, bool flipY)
+bool DrawingBuffer::copyToPlatformTexture(blink::WebGraphicsContext3D* context, Platform3DObject texture, GLenum internalFormat, GLenum destType, GLint level, bool premultiplyAlpha, bool flipY, bool fromFrontBuffer)
 {
     if (!m_context->makeContextCurrent())
         return false;
+
+    GLint textureId = m_colorBuffer.textureId;
+    if (fromFrontBuffer)
+        textureId = m_frontColorBuffer.textureId;
+
     if (m_contentsChanged) {
         if (m_multisampleMode != None) {
             commit();
             if (!m_framebufferBinding)
                 bind();
             else
                 restoreFramebufferBinding();
         }
         m_context->flush();
     }
 
     if (!Extensions3DUtil::canUseCopyTextureCHROMIUM(internalFormat, destType, level))
         return false;
 
     // Contexts may be in a different share group. We must transfer the texture through a mailbox first
     RefPtr<MailboxInfo> bufferMailbox = adoptRef(new MailboxInfo());
     m_context->genMailboxCHROMIUM(bufferMailbox->mailbox.name);
-    m_context->bindTexture(GL_TEXTURE_2D, m_colorBuffer.textureId);
+    m_context->bindTexture(GL_TEXTURE_2D, textureId);
     m_context->produceTextureCHROMIUM(GL_TEXTURE_2D, bufferMailbox->mailbox.name);
     m_context->flush();
 
     bufferMailbox->mailbox.syncPoint = m_context->insertSyncPoint();
 
     if (!context->makeContextCurrent())
         return false;
 
     Platform3DObject sourceTexture = context->createTexture();
 
@@ skipping 604 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 WebCore