https://bugs.webkit.org/show_bug.cgi?id=106854

Reviewed by Darin Adler.

Source/WebCore:

This patch replaces DocumentWeakReference with WeakPtr. There should be
no change in behavior.

* dom/Document.cpp:
(WebCore):
(WebCore::Document::Document):
(WebCore::Document::~Document):
(WebCore::PerformTaskContext::PerformTaskContext):
(PerformTaskContext):
(WebCore::Document::didReceiveTask):
(WebCore::Document::postTask):
(WebCore::Document::reportMemoryUsage):
* dom/Document.h:
(WebCore):
(Document):

Source/WTF:

This patch adds a simple WeakPtr object to WTF. To use WeakPtr, objects
must hold a WeakPtrFactory member variable, which clears the WeakPtrs
when the object is destructed. The underlying storage is a
ThreadSafeRefCounted "WeakReference" object, which is shared by all the
WeakPtrs.

WeakPtr is a generalization of DocumentWeakReference, which is used to
check whether the Document object is alive when tasks arive on the main
thread from worker threads. We plan to use a similar pattern in the
threaded HTML parser, but we want to send tasks to objects other than
Document.

* GNUmakefile.list.am:
* WTF.gypi:
* WTF.pro:
* WTF.vcproj/WTF.vcproj:
* WTF.xcodeproj/project.pbxproj:
* wtf/CMakeLists.txt:
* wtf/WeakPtr.h: Added.
(WeakReference):
    - The ThreadSafeRefCounted object shared by all the WeakPtr
      instances. This patch uses ThreadSafeRefCounted so that we can
      use WeakPtrs to cancel cross-thread messages.
(WTF::WeakReference::create):
(WTF::WeakReference::get):
(WTF::WeakReference::clear):
    - When the object is destroyed, WeakPtrFactory calls this function
      to clear all the WeakPtrs.
(WTF::WeakReference::WeakReference):
(WTF::WeakPtr::WeakPtr):
(WTF::WeakPtr::get):
    - We might want to add implicit conversions and Boolean operators
      in the future, but I've kept this class simple for now.
(WTF::WeakPtrFactory::WeakPtrFactory):
(WTF::WeakPtrFactory::~WeakPtrFactory):
(WTF::WeakPtrFactory::createWeakPtr):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@139780 268f45cc-cd09-0410-ab3c-d52691b4dbfc