[skia_benchmarking_extension] fix off-by-one timing reporting.

skia/ext/benchmarking_canvas.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/containers/hash_tables.h"
 #include "base/logging.h"
 #include "base/time/time.h"
 #include "skia/ext/benchmarking_canvas.h"
 #include "third_party/skia/include/core/SkDevice.h"
 #include "third_party/skia/include/utils/SkProxyCanvas.h"
@@ skipping 185 matching lines @@
   const BenchmarkingCanvas* tracking_canvas_;
 };
 
 AutoStamper::AutoStamper(TimingCanvas *timing_canvas)
     : timing_canvas_(timing_canvas) {
   start_ticks_ = base::TimeTicks::HighResNow();
 }
 
 AutoStamper::~AutoStamper() {
   base::TimeDelta delta = base::TimeTicks::HighResNow() - start_ticks_;
-  int command_index = timing_canvas_->tracking_canvas_->CommandCount();
+  int command_index = timing_canvas_->tracking_canvas_->CommandCount() - 1;
+  DCHECK_GE(command_index, 0);
   timing_canvas_->timings_map_[command_index] = delta;
 }
 
 BenchmarkingCanvas::BenchmarkingCanvas(int width, int height)
     : SkNWayCanvas(width, height) {
   debug_canvas_ = skia::AdoptRef(SkNEW_ARGS(SkDebugCanvas, (width, height)));
   timing_canvas_ = skia::AdoptRef(SkNEW_ARGS(TimingCanvas, (width, height, this)));
 
   addCanvas(debug_canvas_.get());
   addCanvas(timing_canvas_.get());
@@ skipping 11 matching lines @@
   DCHECK_LT(index, static_cast<size_t>(debug_canvas_->getSize()));
   return debug_canvas_->getDrawCommandAt(index);
 }
 
 double BenchmarkingCanvas::GetTime(size_t index) {
   DCHECK_LT(index,  static_cast<size_t>(debug_canvas_->getSize()));
   return timing_canvas_->GetTime(index);
 }
 
 } // namespace skia