Speed up fix for expando-loss conformance test.

third_party/WebKit/Source/modules/webgl/WebGLObject.h

 /*
  * 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 38 matching lines @@
 }
 
 template <typename T>
 GLuint objectNonZero(const T* object)
 {
     GLuint result = object->object();
     DCHECK(result);
     return result;
 }
 
+// TODO(kbr): v8::Persistent doesn't auto-reset in its destructor,
+// which wreaks havoc when they're embedded in Oilpan objects even if
+// they use GarbageCollectedFinalized. The first V8 GC after the
+// Oilpan object is reclaimed will reset the cell in the
+// v8::Persistent, scribbling over the Oilpan heap. If v8::Persistents
+// are ever embedded in Oilpan objects, they must use
+// CopyablePersistentTraits to pick up the kResetInDestructor = true
+// setting. This alias template ensures correct usage, but ideally,
+// these persistent caches would not be necessary. crbug.com/611864
+template <typename T>
+using V8CopyablePersistent = v8::Persistent<T, v8::CopyablePersistentTraits<T>>;

[haraken, 2016/05/15 09:18:46]

Instead you should use ScopedPersistent. Then ScopedPersistent's destructor
resets the underlying persistent handle, which will solve the problem.

+
 class WebGLObject : public GarbageCollectedFinalized<WebGLObject>, public ScriptWrappable {
 public:
     virtual ~WebGLObject();
 
     // deleteObject may not always delete the OpenGL resource.  For programs and
     // shaders, deletion is delayed until they are no longer attached.
     // FIXME: revisit this when resource sharing between contexts are implemented.
     void deleteObject(gpu::gles2::GLES2Interface*);
 
     void onAttached() { ++m_attachmentCount; }
@@ skipping 25 matching lines @@
     virtual gpu::gles2::GLES2Interface* getAGLInterface() const = 0;
 
 private:
     unsigned m_attachmentCount;
     bool m_deleted;
 };
 
 } // namespace blink
 
 #endif // WebGLObject_h