Add override to Bitmap_GrTextureParamsAdjuster::refOriginalTexture

TBR=caryclark@google.com

Review URL: https://codereview.chromium.org/1417553002 .

src/gpu/SkGr.cpp

@@ -291,7 +291,7 @@ public:
     }
 
 protected:
-    GrTexture* refOriginalTexture(GrContext* ctx) {
+    GrTexture* refOriginalTexture(GrContext* ctx) override {
         GrTexture* tex = fBitmap.getTexture();
         if (tex) {
             return SkRef(tex);