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

cc/trees/latency_info_swap_promise_monitor.cc

Index: cc/trees/latency_info_swap_promise_monitor.cc
diff --git a/cc/trees/latency_info_swap_promise_monitor.cc b/cc/trees/latency_info_swap_promise_monitor.cc
index 6e9c57e04231de38b459c04c7705fff827aa335f..1dc6ef8856f5408b6d511ccb509392273182535a 100644
--- a/cc/trees/latency_info_swap_promise_monitor.cc
+++ b/cc/trees/latency_info_swap_promise_monitor.cc
@@ -59,7 +59,12 @@ void LatencyInfoSwapPromiseMonitor::OnSetNeedsCommitOnMain() {
 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());
   }
 }