cc: Measure compositor timing with finer granularity

cc/trees/layer_tree_host_impl.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_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <map>
 #include <set>
@@ skipping 414 matching lines @@
   AnimateScrollbars(monotonic_time);
   AnimateTopControls(monotonic_time);
 }
 
 void LayerTreeHostImpl::PrepareTiles() {
   if (!tile_manager_)
     return;
   if (!tile_priorities_dirty_)
     return;
 
+  client_->WillPrepareTiles();
   tile_priorities_dirty_ = false;
   tile_manager_->PrepareTiles(global_tile_state_);
-
   client_->DidPrepareTiles();
 }
 
 void LayerTreeHostImpl::StartPageScaleAnimation(
     const gfx::Vector2d& target_offset,
     bool anchor_point,
     float page_scale,
     base::TimeDelta duration) {
   if (!InnerViewportScrollLayer())
     return;
@@ skipping 3138 matching lines @@
     const gfx::ScrollOffset& scroll_offset) {
   if (tree_type == LayerTreeType::ACTIVE) {
     SetTreeLayerScrollOffsetMutated(layer_id, active_tree(), scroll_offset);
   } else {
     SetTreeLayerScrollOffsetMutated(layer_id, pending_tree(), scroll_offset);
     SetTreeLayerScrollOffsetMutated(layer_id, recycle_tree(), scroll_offset);
   }
 }
 
 }  // namespace cc