nanobench: support GMs-as-benches

bench/GMBench.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GMBench.h"
 
 GMBench::GMBench(skiagm::GM* gm) : fGM(gm) {
-    fName.printf("GM:%s", gm->getName());
+    fName.printf("GM_%s", gm->getName());
 }
 
 GMBench::~GMBench() { delete fGM; }
 
 const char* GMBench::onGetName() {
     return fName.c_str();
 }
 
 bool GMBench::isSuitableFor(Backend backend) {
     uint32_t flags = fGM->getFlags();
@@ skipping 20 matching lines @@
     fGM->drawBackground(canvas);
     for (int i = 0; i < loops; ++i) {
         fGM->drawContent(canvas);
     }
 }
 
 SkIPoint GMBench::onGetSize() {
     SkISize size = fGM->getISize();
     return SkIPoint::Make(size.fWidth, size.fHeight);
 }