2013-12-30  Antonio Gomes  <a1.gomes@sisa.samsung.com>

        Implement WebCL::releaseAll
        Issue #355

        Reviewed by Igor.

        Similarly to how it was implemented to WebCLContext,
        WebCL singleton class now stores all descendant
        WebCLContext objects it creates, and walks over the list
        in order to call releaseAll down hill.

        The objects stored are weak references, and can be null.

        * Modules/webcl/WebCL.cpp:
        (WebCore::WebCL::createContext):
        (WebCore::WebCL::trackReleaseableWebCLObject):
        (WebCore::WebCL::releaseAll):
        * Modules/webcl/WebCL.h:
        * Modules/webcl/WebCL.idl:
        * Modules/webcl/WebCLContext.cpp:
        (WebCore::WebCLContext::create):
        (WebCore::WebCLContext::WebCLContext):
        * Modules/webcl/WebCLContext.h: