Implement scroll handler latency tracking

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 <string>
 
 #include "base/atomic_sequence_num.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/layer_animation_controller.h"
+#include "cc/base/latency_info_swap_promise.h"
 #include "cc/base/math_util.h"
 #include "cc/debug/devtools_instrumentation.h"
 #include "cc/debug/rendering_stats_instrumentation.h"
 #include "cc/input/top_controls_manager.h"
 #include "cc/layers/heads_up_display_layer.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/layer_iterator.h"
 #include "cc/layers/painted_scrollbar_layer.h"
 #include "cc/layers/render_surface.h"
@@ skipping 976 matching lines @@
     occlusion_tracker.LeaveLayer(it);
   }
 
   in_paint_layer_contents_ = false;
 }
 
 void LayerTreeHost::ApplyScrollAndScale(const ScrollAndScaleSet& info) {
   if (!root_layer_.get())
     return;
 
+  for (size_t i = 0; i < info.latency_infos.size(); ++i) {
+    ui::LatencyInfo latency_info = info.latency_infos[i];
+    if (!latency_info.FindLatency(

[Yufeng Shen (Slow to review), 2014/07/04 18:34:34]

why do we need this check ?

[Sami, 2014/07/07 14:28:18]

Ah, you're right, the latency infos can only flow though here once so there's no
need for this check.

+            ui::INPUT_EVENT_LATENCY_SCROLL_UPDATE_BLINK_COMPONENT, 0, 0)) {
+      latency_info.AddLatencyNumber(
+          ui::INPUT_EVENT_LATENCY_SCROLL_UPDATE_BLINK_COMPONENT, 0, 0);

[Yufeng Shen (Slow to review), 2014/07/04 18:34:34]

Are we planning to use this new component anywhere ?
If we only care about end-to-end latency, then we don't need this new component.
Or do you plan to use this component to derive any new metrics ?

[Sami, 2014/07/07 14:28:18]

Yeah, end-to-end is what really matters here. I wasn't planning to use the new
component for anything in particular, so let's just remove it.

+      TRACE_EVENT_FLOW_STEP0("input",
+                             "LatencyInfo.Flow",
+                             TRACE_ID_DONT_MANGLE(latency_info.trace_id),
+                             "Blink");
+      scoped_ptr<SwapPromise> swap_promise(
+          new LatencyInfoSwapPromise(latency_info));
+      QueueSwapPromise(swap_promise.Pass());
+    }
+  }
+
   gfx::Vector2d inner_viewport_scroll_delta;
   gfx::Vector2d outer_viewport_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 == outer_viewport_scroll_layer_.get()) {
@@ skipping 228 matching lines @@
   swap_promise_list_.push_back(swap_promise.Pass());
 }
 
 void LayerTreeHost::BreakSwapPromises(SwapPromise::DidNotSwapReason reason) {
   for (size_t i = 0; i < swap_promise_list_.size(); i++)
     swap_promise_list_[i]->DidNotSwap(reason);
   swap_promise_list_.clear();
 }
 
 }  // namespace cc