Add mock context and use in ResourceCacheTest.

include/gpu/GrContext.h

Index: include/gpu/GrContext.h
diff --git a/include/gpu/GrContext.h b/include/gpu/GrContext.h
index 464f36d1239e04660d4cdd7d9271fcc2d7d227be..2adc84211a5c97cc7e7eb3f71ee48163a9ab5f90 100644
--- a/include/gpu/GrContext.h
+++ b/include/gpu/GrContext.h
@@ -63,6 +63,11 @@ public:
      */
     static GrContext* Create(GrBackend, GrBackendContext, const Options* opts = NULL);
 
+    /**
+     * Only defined in test apps.
+     */
+    static GrContext* CreateMockContext();
+
     virtual ~GrContext();
 
     /**
@@ -978,6 +983,8 @@ private:
 
     GrContext(const Options&); // init must be called after the constructor.
     bool init(GrBackend, GrBackendContext);
+    void initMockContext();
+    void initCommon();
 
     void setupDrawBuffer();