2013-04-22  Antonio Gomes  <a1.gomes@sisa.samsung.com>

        Implement CL-GL as an extension (part 6)
        Issue #210

        Reviewed by NOBODY (OOPS!).

        Underlying /platform support for "compute extensions".

        Patch follows the logic that Extensions3D has to support
        WebGL/OpenGL{ES} extensions. This is the first out of 3 patches.

        In this first patch, it is added support for querying about
        WebCL global extensions, i.e. extensions available to all
        platform, all devices. So two methods now work correctly:

        - WebCL::getExtension
        - WebCL::getSupportedExtension

        The logic within cacheGlobalExtensions is as following:
        0) Get all OpenCL platforms available.
        1) Get the extensions available in the first platform,
           adding them to a Hash.
        2) If there is only this OpenCL platform available (common
           case), we are done. Bail out!
        3) For any other platform available, check the intersection
           of extensions supported.
        4) In the end, the Hash has only extensions supported by all platforms.

        Patch also adds stubs for the 'support' overload methods,
        for platform and device scopes.

        * Modules/webcl/WebCL.cpp:
        (WebCore::WebCL::getSupportedExtensions):
        * WebCore.xcodeproj/project.pbxproj:
        * bindings/js/JSWebCLCustom.cpp:
        (WebCore::JSWebCL::getSupportedExtensions):
        * platform/opencl/ExtensionsCL.cpp: Added.
        (WebCore):
        (WebCore::ExtensionsCL::get):
        (WebCore::ExtensionsCL::ExtensionsCL):
        (WebCore::ExtensionsCL::~ExtensionsCL):
        (WebCore::ExtensionsCL::supports):
        (WebCore::ExtensionsCL::initializeGlobalExtensions):
        (WebCore::ExtensionsCL::supportsExtension):
        (WebCore::ExtensionsCL::cacheGlobalExtensions):
        * platform/opencl/ExtensionsCL.h: Added.
        (WebCore):
        (ExtensionsCL):