2014-03-10  Antonio Gomes  <a1.gomes@sisa.samsung.com>

        Create a caching mechanism to map CCDeviceID to ComputeDevice
        Issue #470

        Reviewed by TrustMe.

        OpenCL runtime returns the same CCDeviceID (handle to a CL device) whenever queried.
        Given that we wrap CCDeviceID objects with a ComputeDevice class now,
        we should make sure each CCDeviceID is wrapped by the same ComputeDevice
        object, keeping the analogy for the callers.

        Same applies to CCPlatformID and ComputePlatform.

        * platform/ComputeDevice.h:
        * platform/ComputePlatform.h:
        * platform/opencl/ComputeDeviceCL.cpp:
        (WebCore::computeDevicePool):
        (WebCore::ComputeDevice::create):
        * platform/opencl/ComputePlatformCL.cpp:
        (WebCore::computePlatformPool):
        (WebCore::ComputePlatform::create):
        (WebCore::ComputePlatform::getPlatformIDs):
        (WebCore::ComputePlatform::getDeviceIDs):