Oilpan: have History on the heap by default.

Source/core/frame/History.h

Index: Source/core/frame/History.h
diff --git a/Source/core/frame/History.h b/Source/core/frame/History.h
index 12057e486d715a616108d72dc46ff64bfd8c2c89..80a0de1aa92b62a5c97436674bbb5569ae25e544 100644
--- a/Source/core/frame/History.h
+++ b/Source/core/frame/History.h
@@ -32,8 +32,6 @@
 #include "core/frame/DOMWindowProperty.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Forward.h"
-#include "wtf/PassRefPtr.h"
-#include "wtf/RefCounted.h"
 
 namespace blink {
 
@@ -42,13 +40,13 @@ class KURL;
 class ExecutionContext;
 class ExceptionState;
 
-class History final : public RefCountedWillBeGarbageCollectedFinalized<History>, public ScriptWrappable, public DOMWindowProperty {
+class History final : public GarbageCollectedFinalized<History>, public ScriptWrappable, public DOMWindowProperty {
     DEFINE_WRAPPERTYPEINFO();
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(History);

[haraken, 2015/04/24 12:43:52]

WILL_BE_USING_GARBAGE_COLLECTED_MIXIN => USING_GARBAGE_COLLECTED_MIXIN

Here, again, we need to make sure that it is safe to move History to Oilpan
without moving DOMWindowProperty to Oilpan.

The only guy who traces DOMWindowProperty is LocalDOMWindow, and the
LocalDOMWindow is tracing the DOMWindowProperty weakly (not strongly). Thus it
is safe to move History to Oilpan without moving DOMWindowProperty as long as we
keep the pointer-clear-out code as is.

So this CL looks safe.

[sof, 2015/04/24 12:46:41]

I'm not quite sure what to make of the "=>" at the top -- it needs to be
WILL_BE, as DOMWindowProperty is WillBeGarbageCollectedMixin.

[haraken, 2015/04/24 12:47:28]

ah, right. We need to drop the WillBe when dropping the WillBe from
DOMWindowProperty.

 public:
-    static PassRefPtrWillBeRawPtr<History> create(LocalFrame* frame)
+    static History* create(LocalFrame* frame)
     {
-        return adoptRefWillBeNoop(new History(frame));
+        return new History(frame);
     }
 
     unsigned length() const;