cc: Avoid expensive RenderingStats collection.

cc/content_layer_updater.cc

 // Copyright 2011 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 "cc/content_layer_updater.h"
 
 #include "base/debug/trace_event.h"
 #include "base/time.h"
 #include "cc/layer_painter.h"
 #include "cc/rendering_stats.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkPaint.h"
 #include "third_party/skia/include/core/SkRect.h"
 #include "third_party/skia/include/core/SkScalar.h"
 #include "ui/gfx/rect_conversions.h"
 #include "ui/gfx/rect_f.h"
 
 namespace cc {
 
 ContentLayerUpdater::ContentLayerUpdater(scoped_ptr<LayerPainter> painter)
     : m_painter(painter.Pass())
 {
 }
 
 ContentLayerUpdater::~ContentLayerUpdater()
 {
 }
 
-void ContentLayerUpdater::paintContents(SkCanvas* canvas, const gfx::Rect& contentRect, float contentsWidthScale, float contentsHeightScale, gfx::Rect& resultingOpaqueRect, RenderingStats& stats)
+void ContentLayerUpdater::paintContents(SkCanvas* canvas, const gfx::Rect& contentRect, float contentsWidthScale, float contentsHeightScale, gfx::Rect& resultingOpaqueRect, RenderingStats* stats)
 {
     TRACE_EVENT0("cc", "ContentLayerUpdater::paintContents");
     canvas->save();
     canvas->translate(SkFloatToScalar(-contentRect.x()), SkFloatToScalar(-contentRect.y()));
 
     gfx::Rect layerRect = contentRect;
 
     if (contentsWidthScale != 1 || contentsHeightScale != 1) {
         canvas->scale(SkFloatToScalar(contentsWidthScale), SkFloatToScalar(contentsHeightScale));
 
         gfx::RectF rect = gfx::ScaleRect(contentRect, 1 / contentsWidthScale, 1 / contentsHeightScale);
         layerRect = gfx::ToEnclosingRect(rect);
     }
 
     SkPaint paint;
     paint.setAntiAlias(false);
     paint.setXfermodeMode(SkXfermode::kClear_Mode);
     SkRect layerSkRect = SkRect::MakeXYWH(layerRect.x(), layerRect.y(), layerRect.width(), layerRect.height());
     canvas->drawRect(layerSkRect, paint);
     canvas->clipRect(layerSkRect);
 
     gfx::RectF opaqueLayerRect;
-    base::TimeTicks paintBeginTime = base::TimeTicks::Now();
+    base::TimeTicks paintBeginTime;
+    if (stats)
+        paintBeginTime = base::TimeTicks::Now();
     m_painter->paint(canvas, layerRect, opaqueLayerRect);
-    stats.totalPaintTime += base::TimeTicks::Now() - paintBeginTime;
+    if (stats) {
+        stats->totalPaintTime += base::TimeTicks::Now() - paintBeginTime;
+        stats->totalPixelsPainted += contentRect.width() * contentRect.height();
+    }
     canvas->restore();
 
-    stats.totalPixelsPainted += contentRect.width() * contentRect.height();
-
     gfx::RectF opaqueContentRect = gfx::ScaleRect(opaqueLayerRect, contentsWidthScale, contentsHeightScale);
     resultingOpaqueRect = gfx::ToEnclosedRect(opaqueContentRect);
 
     m_contentRect = contentRect;
 }
 
 }  // namespace cc