Oilpan: add missing leftmost trace()s for GC mixins.

Source/web/WebRemoteFrameImpl.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WebRemoteFrameImpl_h
 #define WebRemoteFrameImpl_h
 
 #include "core/frame/FrameOwner.h"
 #include "platform/heap/Handle.h"
 #include "public/web/WebRemoteFrame.h"
@@ skipping 10 matching lines @@
 class RemoteFrame;
 
 // FIXME: This is just a placeholder frame owner to supply to RemoteFrame when
 // the parent is also a remote frame. Strictly speaking, this shouldn't be
 // necessary, since a remote frame shouldn't ever need to communicate with a
 // remote parent (there are no sandbox flags to retrieve in this case, nor can
 // the RemoteFrame itself load a document). In most circumstances, the check for
 // frame->owner() can be replaced with a check for frame->tree().parent(). Once
 // that's done, this class can be removed.
 class PlaceholderFrameOwner : public NoBaseWillBeGarbageCollectedFinalized<PlaceholderFrameOwner>, public FrameOwner {
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(PlaceholderFrameOwner);

[dcheng, 2015/01/06 23:06:44]

Out of curiosity, why do we need a mixin at all here? FrameOwner has no data
members at all.

[haraken, 2015/01/07 01:44:41]

Hmm, you're right. I don't see any reason FrameOwner needs to be a mixin
either... Sigbjorn, can we de-mixin FrameOwner in a follow-up CL?

[sof, 2015/01/07 06:18:01]

Yes, well caught -- will remove that.

It depends on style to some extent, but something like

class A : public GarbageCollectedMixin { };
class B : public A { public: Member<A> m_a; };
class C : public GarbageCollected<C>, public B {
USING_GARBAGE_COLLECTED_MIXIN(C); ... };

would benefit from using GCMixin as a base for A, irrespective of A having GC
references or not.

 public:
     virtual bool isLocal() const override;
     virtual SandboxFlags sandboxFlags() const override;
     virtual void dispatchLoad() override;
+
+    virtual void trace(Visitor*) override;
 };
 
 class WebRemoteFrameImpl final : public RefCountedWillBeGarbageCollectedFinalized<WebRemoteFrameImpl>, public WebRemoteFrame {
 public:
     explicit WebRemoteFrameImpl(WebRemoteFrameClient*);
     virtual ~WebRemoteFrameImpl();
 
     // WebRemoteFrame methods.
     virtual bool isWebLocalFrame() const override;
     virtual WebLocalFrame* toWebLocalFrame() override;
@@ skipping 177 matching lines @@
     GC_PLUGIN_IGNORE("340522")
     Persistent<WebRemoteFrameImpl> m_selfKeepAlive;
 #endif
 };
 
 DEFINE_TYPE_CASTS(WebRemoteFrameImpl, WebFrame, frame, frame->isWebRemoteFrame(), frame.isWebRemoteFrame());
 
 } // namespace blink
 
 #endif // WebRemoteFrameImpl_h