Test abandoning GL context in dm/nanobench.

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 30 matching lines @@
 public:
     typedef int GLContextType;
 
     static const GLContextType kANGLE_GLContextType  = 0,
                                kDebug_GLContextType  = 0,
                                kMESA_GLContextType   = 0,
                                kNVPR_GLContextType   = 0,
                                kNative_GLContextType = 0,
                                kNull_GLContextType   = 0;
     void destroyContexts() {}
+
+    void abandonContexts() {}
 };
 
 namespace DM {
 
 static const bool kGPUDisabled = true;
 
 static inline SkSurface* NewGpuSurface(GrContextFactory*,
                                        GrContextFactory::GLContextType,
                                        GrGLStandard,
                                        SkImageInfo,
                                        int) {
     return NULL;
 }
 
 }  // namespace DM
 
 #endif//SK_SUPPORT_GPU
 
 #endif//DMGpuSupport_DEFINED