2014-03-06  Sharath Kamath  <s.kamath@samsung.com>

        Add switch for KHR_gl_sharing extension in WebCL.

        Fixed #466

        Reviewed by Antonio.

        Add a switch to turn on and off the KHR_gl_sharing API's.
        Without calling enableExtension("KHR_gl_sharing") the API must
        throw WEBCL_EXTENSION_NOT_ENABLED exception.

        Also moving the caching extension logic to the WebCLContext::create() API.

        All test cases under KHR_gl_sharing folder in extensions.

        * Modules/webcl/WebCLCommandQueue.cpp:
        (WebCore::WebCLCommandQueue::enqueueAcquireGLObjects):
        (WebCore::WebCLCommandQueue::enqueueReleaseGLObjects):
        * Modules/webcl/WebCLContext.cpp:
        (WebCore::WebCLContext::create):
        (WebCore::WebCLContext::WebCLContext):
        (WebCore::WebCLContext::createFromGLBuffer):
        (WebCore::WebCLContext::createFromGLRenderbuffer):
        (WebCore::WebCLContext::createFromGLTexture):
        * Modules/webcl/WebCLContext.h:
        * Modules/webcl/WebCLMemoryObject.cpp:
        (WebCore::WebCLMemoryObject::isExtensionEnabled):
        (WebCore::WebCLMemoryObject::getGLObjectInfo):
        * Modules/webcl/WebCLMemoryObject.h: