Refactor SkGLContext to be actually extendable

include/gpu/gl/SkDebugGLContext.h

Index: include/gpu/gl/SkDebugGLContext.h
diff --git a/include/gpu/gl/SkDebugGLContext.h b/include/gpu/gl/SkDebugGLContext.h
index 792666332ee3cc1034e921e519411a7c2caad02e..ad157fa653dfa7f267cbf4beb0c62662d09eef6f 100644
--- a/include/gpu/gl/SkDebugGLContext.h
+++ b/include/gpu/gl/SkDebugGLContext.h
@@ -11,17 +11,19 @@
 #include "SkGLContext.h"
 
 class SkDebugGLContext : public SkGLContext {
-
 public:
-    SkDebugGLContext() {}
-
+    virtual ~SkDebugGLContext() SK_OVERRIDE;
     virtual void makeCurrent() const SK_OVERRIDE {}
     virtual void swapBuffers() const SK_OVERRIDE {}
 
-protected:
-    virtual const GrGLInterface* createGLContext(GrGLStandard forcedGpuAPI) SK_OVERRIDE;
-
-    virtual void destroyGLContext() SK_OVERRIDE {};
+    static SkDebugGLContext* Create(GrGLStandard forcedGpuAPI) {
+        if (kGLES_GrGLStandard == forcedGpuAPI) {
+            return NULL;
+        }
+        return SkNEW(SkDebugGLContext);
+    }
+private:
+    SkDebugGLContext();
 };
 
 #endif