Add compositor support for the LatencyInfo.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 81f905199febf1e9ff9f533074e8fd8e37215487..e177fb1e96221c994419193c10d329e826a86fe4 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -253,6 +253,8 @@ void LayerTreeHost::Layout() {
 void LayerTreeHost::BeginCommitOnImplThread(LayerTreeHostImpl* host_impl) {
   DCHECK(proxy_->IsImplThread());
   TRACE_EVENT0("cc", "LayerTreeHost::CommitTo");
+  host_impl->SetLatencyInfo(latency_info_);

[jamesr, 2013/04/17 23:15:21]

To make this work in impl-side painting you want to associate the latency
information with a LayerTreeImpl, not with a LayerTreeHostImpl.  Impl-side
painting works by doing this:

LayerTreeHost pushes info to the LayerTreeHostImpl::pending_tree_, which is a
LayerTreeImpl
then when the pending tree has rasterized enough
LayerTreeHostImpl pushes the pending_tree_ into its active_tree_

LayerTreeHostImpl always draws (swaps) from its active_tree_.

I think it's easy enough to put this information on the LayerTreeImpl from the
start, so can we do that in this patch?  See the 'sync_tree_' in
FinishCommitOnImplThread() below

+  latency_info_.Clear();
 }
 
 // This function commits the LayerTreeHost to an impl tree. When modifying
@@ -675,6 +677,10 @@ void LayerTreeHost::SetVisible(bool visible) {
   proxy_->SetVisible(visible);
 }
 
+void LayerTreeHost::SetLatencyInfo(const LatencyInfo& latency_info) {
+  latency_info_.MergeWith(latency_info);
+}
+
 void LayerTreeHost::StartPageScaleAnimation(gfx::Vector2d target_offset,
                                             bool use_anchor,
                                             float scale,