Add visualbench option for nvpr stencil samples

tools/VisualBench/VisualBench.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  */
 
 #include "VisualBench.h"
 
@@ skipping 85 matching lines @@
         SkFAIL("Could not create backend\n");
     }
 
     this->setVsync(false);
 
     fSurface.reset(nullptr);
 
     fInterface.reset(GrGLCreateNativeInterface());
 
     // TODO use the GLContext creation factories and also set this all up in configs
-    if (!FLAGS_nvpr) {
+    if (0 == FLAGS_nvpr) {
         fInterface.reset(GrGLInterfaceRemoveNVPR(fInterface));
     }
     SkASSERT(fInterface);
 
     // setup contexts
     fContext.reset(GrContext::Create(kOpenGL_GrBackend, (GrBackendContext)fInterface.get()));
     SkASSERT(fContext);
 
     // setup rendertargets
     this->setupRenderTarget();
@@ skipping 53 matching lines @@
 }
 
 void application_term() {
     SkEvent::Term();
 }
 
 SkOSWindow* create_sk_window(void* hwnd, int argc, char** argv) {
     return new VisualBench(hwnd, argc, argv);
 }