Read compositor VSync information from platform, when possible

ash/display/display_change_observer_chromeos.cc

Index: ash/display/display_change_observer_chromeos.cc
diff --git a/ash/display/display_change_observer_chromeos.cc b/ash/display/display_change_observer_chromeos.cc
index 7c5780ec639259df80a29f85ee6698482fa9985f..7da0c679c611d06455605b909ace4fa054da1f71 100644
--- a/ash/display/display_change_observer_chromeos.cc
+++ b/ash/display/display_change_observer_chromeos.cc
@@ -41,7 +41,9 @@ const float kInchInMm = 25.4f;
 // one comes first.
 struct ResolutionSorter {
   bool operator()(const Resolution& a, const Resolution& b) {
-    return a.size.width() * a.size.height() > b.size.width() * b.size.height();
+    if (a.size.GetArea() == b.size.GetArea())
+      return (a.refresh_rate > b.refresh_rate);
+    return (a.size.GetArea() > b.size.GetArea());
   }
 };
 
@@ -58,6 +60,7 @@ std::vector<Resolution> DisplayChangeObserver::GetResolutionList(
     const OutputConfigurator::ModeInfo& mode_info = it->second;
     const std::pair<int, int> size(mode_info.width, mode_info.height);
     const Resolution resolution(gfx::Size(mode_info.width, mode_info.height),
+                                mode_info.refresh_rate,
                                 mode_info.interlaced);
 
     // Add the resolution if it isn't already present and override interlaced
@@ -104,10 +107,14 @@ chromeos::OutputState DisplayChangeObserver::GetStateForDisplayIds(
 
 bool DisplayChangeObserver::GetResolutionForDisplayId(int64 display_id,
                                                       int* width,
-                                                      int* height) const {
+                                                      int* height,
+                                                      float* refresh_rate)
+    const {
   gfx::Size resolution;
-  if (!Shell::GetInstance()->display_manager()->
-      GetSelectedResolutionForDisplayId(display_id, &resolution)) {
+  if (!Shell::GetInstance()
+           ->display_manager()
+           ->GetSelectedResolutionForDisplayId(
+                 display_id, &resolution, refresh_rate)) {
     return false;
   }
 
@@ -145,9 +152,7 @@ void DisplayChangeObserver::OnDisplayModeChanged(
     gfx::Rect display_bounds(
         output.x, output.y, mode_info->width, mode_info->height);
 
-    std::vector<Resolution> resolutions;
-    if (output.type != chromeos::OUTPUT_TYPE_INTERNAL)
-      resolutions = GetResolutionList(output);
+    std::vector<Resolution> resolutions = GetResolutionList(output);
 
     std::string name = output.type == chromeos::OUTPUT_TYPE_INTERNAL ?
         l10n_util::GetStringUTF8(IDS_ASH_INTERNAL_DISPLAY_NAME) :