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 977 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() || info.page_scale_delta != 1.0f;
+
+  if (has_scrolls) {
+    // We use async events here because we want to conditionally trace. This
+    // is too spammy otherwise.
+    TRACE_EVENT_ASYNC_BEGIN0(

[dsinclair, 2013/08/08 17:30:14]

Why not TRACE_EVENT_BEGIN0 and END0 below?

+        "impl-scroll",
+        "LayerTreeHost::ApplyScrollAndScale",
+        this);
+  }
+
   gfx::Vector2d root_scroll_delta;
   Layer* root_scroll_layer = FindFirstScrollableLayer(root_layer_.get());
 
   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) {
@@ skipping 12 matching lines @@
     // Preemptively apply the scroll offset and scale delta here before sending
     // it to the client.  If the client comes back and sets it to the same
     // value, then the layer can early out without needing a full commit.
     if (root_scroll_layer) {
       root_scroll_layer->SetScrollOffsetFromImplSide(
           root_scroll_layer->scroll_offset() + root_scroll_delta);
     }
     ApplyPageScaleDeltaFromImplSide(info.page_scale_delta);
     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 132 matching lines @@
 void LayerTreeHost::DidLoseUIResources() {
   // When output surface is lost, we need to recreate the resource.
   for (UIResourceClientMap::iterator iter = ui_resource_client_map_.begin();
        iter != ui_resource_client_map_.end();
        ++iter) {
     UIResourceLost(iter->first);
   }
 }
 
 }  // namespace cc