Return a transparent black ImageBitmap when mailbox is invalid

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 624 matching lines @@
 {
     shouldFailContextCreationForTesting = true;
 }
 
 ImageBitmap* WebGLRenderingContextBase::transferToImageBitmapBase()
 {
     if (!drawingBuffer())
         return nullptr;
     WebExternalTextureMailbox mailbox;
     drawingBuffer()->prepareMailbox(&mailbox, 0);
-    ImageBitmap* imageBitmap = ImageBitmap::create(mailbox);
+    ImageBitmap* imageBitmap;
+    // If the mailbox is invalid, return an transparent black ImageBitmap

[Ken Russell (switch to Gerrit), 2016/07/12 22:52:04]

Could you add a comment saying that the only situation this should happen is
when two or more calls to transferToImageBitmap are made back-to-back?

+    if (mailbox.textureSize.width == 0 && mailbox.textureSize.height == 0) {
+        sk_sp<SkSurface>surface = SkSurface::MakeRasterN32Premul(drawingBuffer()->size().width(), drawingBuffer()->size().height());
+        imageBitmap = ImageBitmap::create(StaticBitmapImage::create(fromSkSp(surface->makeImageSnapshot())));
+    } else {
+        imageBitmap = ImageBitmap::create(mailbox);
+    }
     // TODO(xidachen): Create a small pool of recycled textures from ImageBitmapRenderingContext's
     // transferFromImageBitmap, and try to use them in DrawingBuffer.
     return imageBitmap;
 }
 
 namespace {
 
 // ES2 enums
 static const GLenum kSupportedInternalFormatsES2[] = {
     GL_RGB,
@@ skipping 5827 matching lines @@
         contextGL()->PixelStorei(GL_UNPACK_ALIGNMENT, 1);
 }
 
 void WebGLRenderingContextBase::restoreUnpackParameters()
 {
     if (m_unpackAlignment != 1)
         contextGL()->PixelStorei(GL_UNPACK_ALIGNMENT, m_unpackAlignment);
 }
 
 } // namespace blink