Prepare for remote->local frame swap

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"
 #include "public/web/WebRemoteFrameClient.h"
 #include "web/RemoteFrameClientImpl.h"
 #include "wtf/HashMap.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/RefCounted.h"
 
 namespace blink {
 
 class FrameHost;
 class FrameOwner;
 class RemoteFrame;
 class WebViewImpl;
 
+// 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);
+public:
+    virtual bool isLocal() const override;
+    virtual SandboxFlags sandboxFlags() const override;
+    virtual void dispatchLoad() 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;
     virtual bool isWebRemoteFrame() const override;
     virtual WebRemoteFrame* toWebRemoteFrame() override;
@@ skipping 172 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