Create base class for common functionality of Web{Local,Remote}Frame

third_party/WebKit/Source/web/WebFrameImplBase.h

+// Copyright 2015 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 WebFrameImplBase_h
+#define WebFrameImplBase_h
+
+#include "platform/heap/Handle.h"
+#include "wtf/text/AtomicString.h"
+
+namespace blink {
+
+class Frame;
+class FrameHost;
+class FrameOwner;
+
+// WebFrameImplBase exists to avoid the diamond inheritance problem:
+// - The public interfaces WebLocalFrame/WebRemoteFrame extend WebFrame.
+// - WebLocalFrameImpl implements WebLocalFrame and WebRemoteFrameImpl
+//   implements WebRemoteFrame.
+// - The private implementations should share some functionality, but cannot
+//   inherit from a common base class inheriting WebFrame. This would result in
+//   WebFrame beind inherited from two different base classes.
+//
+// To get around this, only the private implementations have WebFrameImplBase as
+// a base class. WebFrame exposes a virtual accessor to retrieve the underlying
+// implementation as an instance of the base class, but has no inheritance
+// relationship with it. The cost is a virtual indirection, but this is nicer
+// than the previous manual dispatch emulating real virtual dispatch.
+class WebFrameImplBase : public RefCountedWillBeGarbageCollectedFinalized<WebFrameImplBase> {
+public:
+    virtual ~WebFrameImplBase();
+
+    virtual void initializeCoreFrame(FrameHost*, FrameOwner*, const AtomicString& name, const AtomicString& fallbackName) = 0;
+    // TODO(dcheng): Rename this to coreFrame()? This probably also shouldn't be const...
+    virtual Frame* frame() const = 0;
+
+#if ENABLE(OILPAN)

[haraken, 2015/11/24 02:30:53]

I guess ENABLE(OILPAN) won't be needed.

[dcheng, 2015/11/24 06:55:07]

Hmm, is ENABLE(OILPAN) universally enabled? Right now, this still has to be a
WillBe since WebLocalFrameImpl/WebRemoteFrameImpl is a WillBe type. While it's
not strictly needed, it doesn't make sense to have the trace either if oilpan
isn't enabled. Or is this just to make the conversion simpler later?

[haraken, 2015/11/24 07:00:33]

We normally don't add #if ENABLE(OILPAN) to a trace method of a WillBe class.
It's just never called.

[dcheng, 2015/11/24 07:50:24]

Makes sense. Done.

+    DECLARE_VIRTUAL_TRACE();
+#endif
+};
+
+} // namespace blink
+
+#endif // WebFrameImplBase_h