optimize circularclips to act as a bench, fix null-check bug in etcbench

bench/ETCBitmapBench.cpp

Index: bench/ETCBitmapBench.cpp
diff --git a/bench/ETCBitmapBench.cpp b/bench/ETCBitmapBench.cpp
index aaa2ce7a6600411021cceb5213e7e26d85671505..e5ec44f2de820bdb4da78691a81f8e20714ccdb5 100644
--- a/bench/ETCBitmapBench.cpp
+++ b/bench/ETCBitmapBench.cpp
@@ -210,8 +210,11 @@ protected:
     }
 
     virtual void onDraw(const int loops, SkCanvas* canvas) SK_OVERRIDE {
+        SkPixelRef* pr = fBitmap.pixelRef();
         for (int i = 0; i < loops; ++i) {
-            this->fBitmap.pixelRef()->notifyPixelsChanged();
+            if (pr) {
+                pr->notifyPixelsChanged();
+            }
             canvas->drawBitmap(this->fBitmap, 0, 0, NULL);
         }
     }