[wrapper-tracing] Add tracing to WebGLRenderingContextBase and friends

third_party/WebKit/Source/modules/webgl/WebGLFramebuffer.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 527 matching lines @@
     DOMWrapperWorld::setWrapperReferencesInAllWorlds(
         wrapper, attachment.value->object(), isolate);
   }
 }
 
 DEFINE_TRACE(WebGLFramebuffer) {
   visitor->trace(m_attachments);
   WebGLContextObject::trace(visitor);
 }
 
+DEFINE_TRACE_WRAPPERS(WebGLFramebuffer) {
+  for (const auto& attachment : m_attachments) {
+    visitor->traceWrappers(attachment.value->object());

[Michael Lippautz, 2016/10/06 17:54:54]

I mirrored the object grouping behavior here by directly retaining
WebGLAttachment::object(). Should we also keep the intermediate WebGLAttachment?

[Ken Russell (switch to Gerrit), 2016/10/06 19:05:14]

There's no JavaScript wrapper for it, so that's not necessary.

[Michael Lippautz, 2016/10/06 19:58:13]

Yep, it's not necessary. 

I guess my question is whether we should try to avoid shortcuts and follow the
object graph (in this case, make WebGLAttachment tracable and trace the object()
in there), or just mirror what object grouping did.

I am fine with both.

[Ken Russell (switch to Gerrit), 2016/10/07 03:00:55]

Let's just mirror what object grouping did -- i.e., don't add a traceWrappers to
WebGLAttachment. That class is an implementation detail and it makes sense to me
that traceWrappers should really only be added to ScriptWrappables.

[haraken, 2016/10/07 04:48:49]

We've already added a bunch of traceWrappers to non-ScriptWrappables, because we
sometimes need to tell DOM-side reachability to V8.

That being said, I don't have any strong opinion about how
WebGLFramebuffer::traceWrappers should be written. The current CL looks fine.

[Ken Russell (switch to Gerrit), 2016/10/07 04:58:52]

OK. I don't have a strong opinion on this.

+  }
+  WebGLContextObject::traceWrappers(visitor);
+}
+
 }  // namespace blink