More natural way to serialize GPU tasks and tests.

dm/DMGpuSupport.h

 #ifndef DMGpuSupport_DEFINED
 #define DMGpuSupport_DEFINED
 
 // Provides Ganesh to DM,
 // or if it's not available, fakes it enough so most code doesn't have to know that.
 
 #include "SkSurface.h"
 
 #if SK_SUPPORT_GPU
 
@@ skipping 57 matching lines @@
                                        SkImageInfo,
                                        int,
                                        bool) {
     return NULL;
 }
 
 }  // namespace DM
 
 #endif//SK_SUPPORT_GPU
 
-GrContextFactory* GetThreadLocalGrContextFactory();
-
 #endif//DMGpuSupport_DEFINED