Oilpan: fix build after r197063, move HitTestCache to the heap.

Source/core/layout/HitTestResult.h

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  * Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 16 matching lines @@
 #include "core/layout/HitTestRequest.h"
 #include "platform/geometry/FloatQuad.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/LayoutRect.h"
 #include "platform/heap/Handle.h"
 #include "platform/text/TextDirection.h"
 #include "wtf/Forward.h"
 #include "wtf/ListHashSet.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/RefPtr.h"
+#include "wtf/VectorTraits.h"
 
 namespace blink {
 
 class Element;
 class LocalFrame;
 class HTMLAreaElement;
 class HTMLMediaElement;
 class Image;
 class KURL;
 class Node;
@@ skipping 118 matching lines @@
         // determine where inside the layoutObject we hit on subsequent operations.
     RefPtrWillBeMember<Element> m_innerURLElement;
     RefPtrWillBeMember<Scrollbar> m_scrollbar;
     bool m_isOverWidget; // Returns true if we are over a widget (and not in the border/padding area of a LayoutPart for example).
 
     mutable OwnPtrWillBeMember<NodeSet> m_listBasedTestResult;
 };
 
 } // namespace blink
 
+WTF_ALLOW_INIT_WITH_MEM_FUNCTIONS(blink::HitTestResult);

[haraken, 2015/06/13 07:12:21]

The default constructor of blink::HitTestResult is setting  m_hitTestRequest to
HitTestRequest::ReadOnly|HitTestRequest::Active, but is it ok to initialize it
with memset?

[sof, 2015/06/13 12:30:31]

For the one use of HitTestResult in a vector (HitTestCache), it will be. The
alternative is to add a wrapper (heap) object indirection, which is somewhat
tedious.

[sof, 2015/06/13 17:00:03]

Is the HeapVector<> restriction accurate, or is it merely reusing
canInitializeWithMemset for convenience?

i.e., canInitializeWithMemset is used to determine if unused slots can be
cleared with memset(). So that we can guarantee that tracing those slots won't
run into trouble. Unused slots are otherwise not observable, so if they
represent valid objects or not, isn't relevant. Slots will otherwise be
initalize()d correctly.

+
 #endif // HitTestResult_h