Add impl/comp scrolling instrumentation.

cc/trees/layer_tree_host.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/trees/layer_tree_host.h"
 
 #include <algorithm>
 #include <stack>
 
 #include "base/bind.h"
@@ skipping 947 matching lines @@
 
   in_paint_layer_contents_ = false;
 
   occlusion_tracker.overdraw_metrics()->RecordMetrics(this);
 }
 
 void LayerTreeHost::ApplyScrollAndScale(const ScrollAndScaleSet& info) {
   if (!root_layer_.get())
     return;
 
+  const bool has_scrolls = !info.scrolls.empty();

[enne (OOO), 2013/07/29 17:46:31]

...or page scale delta != 1?

+  if (has_scrolls) {
+    // We use async events here because we want to conditionally trace. This
+    // is too spammy otherwise.
+    TRACE_EVENT_ASYNC_BEGIN0(
+        "impl-scroll",
+        "LayerTreeHost::ApplyScrollAndScale",
+        this);
+  }
+
   Layer* root_scroll_layer = FindFirstScrollableLayer(root_layer_.get());
   gfx::Vector2d root_scroll_delta;
 
   for (size_t i = 0; i < info.scrolls.size(); ++i) {
     Layer* layer =
         LayerTreeHostCommon::FindLayerInSubtree(root_layer_.get(),
                                                 info.scrolls[i].layer_id);
     if (!layer)
       continue;
     if (layer == root_scroll_layer) {
       root_scroll_delta += info.scrolls[i].scroll_delta;
     } else {
       layer->SetScrollOffsetFromImplSide(layer->scroll_offset() +
                                          info.scrolls[i].scroll_delta);
     }
   }
   if (!root_scroll_delta.IsZero() || info.page_scale_delta != 1.f)
     client_->ApplyScrollAndScale(root_scroll_delta, info.page_scale_delta);
+
+  if (has_scrolls) {
+    TRACE_EVENT_ASYNC_END0(
+        "impl-scroll",
+        "LayerTreeHost::ApplyScrollAndScale",
+        this);
+  }
 }
 
 void LayerTreeHost::StartRateLimiter(WebKit::WebGraphicsContext3D* context3d) {
   if (animating_)
     return;
 
   DCHECK(context3d);
   RateLimiterMap::iterator it = rate_limiters_.find(context3d);
   if (it != rate_limiters_.end()) {
     it->second->Start();
@@ skipping 79 matching lines @@
   for (AnimationRegistrar::AnimationControllerMap::iterator iter = copy.begin();
        iter != copy.end();
        ++iter) {
     (*iter).second->Animate(monotonic_time);
     bool start_ready_animations = true;
     (*iter).second->UpdateState(start_ready_animations, NULL);
   }
 }
 
 }  // namespace cc