Queue latency info swap promises in a separate already-active queue.

cc/trees/latency_info_swap_promise_monitor.cc

 // Copyright 2013 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/latency_info_swap_promise_monitor.h"
 
 #include "base/threading/platform_thread.h"
 #include "cc/output/latency_info_swap_promise.h"
 #include "cc/trees/layer_tree_host.h"
 #include "cc/trees/layer_tree_host_impl.h"
@@ skipping 41 matching lines @@
 void LatencyInfoSwapPromiseMonitor::OnSetNeedsCommitOnMain() {
   if (AddRenderingScheduledComponent(latency_, true /* on_main */)) {
     scoped_ptr<SwapPromise> swap_promise(new LatencyInfoSwapPromise(*latency_));
     layer_tree_host_->QueueSwapPromise(swap_promise.Pass());
   }
 }
 
 void LatencyInfoSwapPromiseMonitor::OnSetNeedsRedrawOnImpl() {
   if (AddRenderingScheduledComponent(latency_, false /* on_main */)) {
     scoped_ptr<SwapPromise> swap_promise(new LatencyInfoSwapPromise(*latency_));
-    layer_tree_host_impl_->active_tree()->QueueSwapPromise(swap_promise.Pass());
+    // Queue a pinned swap promise on the active tree. This will allow
+    // measurement of the time to the next SwapBuffers(). The swap
+    // promise is pinned so that it is not interrupted by new incoming
+    // activations (which would otherwise break the swap promise).
+    layer_tree_host_impl_->active_tree()->QueuePinnedSwapPromise(
+        swap_promise.Pass());
   }
 }
 
 void LatencyInfoSwapPromiseMonitor::OnForwardScrollUpdateToMainThreadOnImpl() {
   if (AddForwardingScrollUpdateToMainComponent(latency_)) {
     int64 new_sequence_number = 0;
     for (ui::LatencyInfo::LatencyMap::const_iterator it =
              latency_->latency_components().begin();
          it != latency_->latency_components().end(); ++it) {
       if (it->first.first == ui::INPUT_EVENT_LATENCY_BEGIN_RWH_COMPONENT) {
@@ skipping 16 matching lines @@
         *latency_,
         ui::INPUT_EVENT_LATENCY_FORWARD_SCROLL_UPDATE_TO_MAIN_COMPONENT);
     scoped_ptr<SwapPromise> swap_promise(
         new LatencyInfoSwapPromise(new_latency));
     layer_tree_host_impl_->QueueSwapPromiseForMainThreadScrollUpdate(
         swap_promise.Pass());
   }
 }
 
 }  // namespace cc