2013-08-13  Sharath Kamath  <s.kamath@samsung.com>

        Cache WebCLPlatforms in WebCL.h
        Issue #239

        Reviewed by Antonio.

        As WebCL platforms are independent of all other factors,
        it can be cached in WebCL interface. This will prevent creation of WebCLPlatform
        objects each time we call webcl.getPlatforms().

        The commit caches the platforms in WebCL interface. Thus will be recreated only
        on window reload.

        No new tests (OOPS!).

        * Modules/webcl/WebCL.cpp:
        (WebCore::WebCL::getPlatforms):
        * Modules/webcl/WebCL.h: