Replace std::map with base::SmallMap in ui::LatencyInfo

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index 0dc182e3f1ed60396beeae394332b6273574dcd6..bd7c263b43f5451f64ddc6c9621e3e45da89d00f 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -1037,7 +1037,7 @@ void RenderWidget::OnSwapBuffersComplete() {
 }
 
 void RenderWidget::OnHandleInputEvent(const blink::WebInputEvent* input_event,
-                                      ui::LatencyInfo latency_info,
+                                      const ui::LatencyInfo& latency_info,
                                       bool is_keyboard_shortcut) {
   handling_input_event_ = true;
   if (!input_event) {
@@ -1056,10 +1056,11 @@ void RenderWidget::OnHandleInputEvent(const blink::WebInputEvent* input_event,
   TRACE_EVENT_SYNTHETIC_DELAY_BEGIN("blink.HandleInputEvent");
 
   scoped_ptr<cc::SwapPromiseMonitor> latency_info_swap_promise_monitor;
-
+  ui::LatencyInfo swap_latency_info(latency_info);

[Yufeng Shen (Slow to review), 2014/03/13 23:05:44]

So why is pass by reference better than pass by value if you are doing
the copy here anyway ?

I would like to keep the full latencyinfo in the ack since there could be
different components added when the event is processed in impl/main thread. And
in the case if the latencyinfo is not pushed into CompositorFrameMetadata (the
event does not cause any rendering and should be ended when it gets acked back
to browser), we still in browser side have all those components added in
renderer.

[jdduke (slow), 2014/03/13 23:14:07]

Visual Studio doesn't allow pass-by-value formal parameters for data types with
aligned memory (SmallMap).  The function must use a reference for the formal
parameter.

   if (compositor_) {
     latency_info_swap_promise_monitor =
-        compositor_->CreateLatencyInfoSwapPromiseMonitor(&latency_info).Pass();
+        compositor_->CreateLatencyInfoSwapPromiseMonitor(&swap_latency_info)
+            .Pass();
   } else {
     latency_info_.push_back(latency_info);
   }
@@ -1169,7 +1170,7 @@ void RenderWidget::OnHandleInputEvent(const blink::WebInputEvent* input_event,
         new InputHostMsg_HandleInputEvent_ACK(routing_id_,
                                               input_event->type,
                                               ack_result,
-                                              latency_info));
+                                              swap_latency_info));
     if (rate_limiting_wanted && event_type_can_be_rate_limited &&
         frame_pending && !is_hidden_) {
       // We want to rate limit the input events in this case, so we'll wait for