ScreenWin notifies DisplayObserver's when displays changed.

ui/gfx/screen_win.cc

Index: ui/gfx/screen_win.cc
diff --git a/ui/gfx/screen_win.cc b/ui/gfx/screen_win.cc
index 7dff9e90d8c686a899b75dfc1df303eb4f85d53b..7b2fcc3aa3f8569aadda44bef0fd6d74d3b03ace 100644
--- a/ui/gfx/screen_win.cc
+++ b/ui/gfx/screen_win.cc
@@ -15,6 +15,10 @@
 
 namespace {
 
+// The delay to handle the display changes notifications.
+// See comments in ScreenWin::OnDisplayChanged.
+const int64 kConfigureDelayMs = 500;
+
 MONITORINFOEX GetMonitorInfoForMonitor(HMONITOR monitor) {
   MONITORINFOEX monitor_info;
   ZeroMemory(&monitor_info, sizeof(MONITORINFOEX));
@@ -24,7 +28,6 @@ MONITORINFOEX GetMonitorInfoForMonitor(HMONITOR monitor) {
 }
 
 gfx::Display GetDisplay(MONITORINFOEX& monitor_info) {
-  // TODO(oshima): Implement Observer.
   int64 id = static_cast<int64>(
       base::Hash(base::WideToUTF8(monitor_info.szDevice)));
   gfx::Rect bounds = gfx::Rect(monitor_info.rcMonitor);
@@ -79,6 +82,7 @@ BOOL CALLBACK EnumMonitorCallback(HMONITOR monitor,
 namespace gfx {
 
 ScreenWin::ScreenWin() {
+  displays_ = BuildDisplays();
 }
 
 ScreenWin::~ScreenWin() {
@@ -111,10 +115,7 @@ int ScreenWin::GetNumDisplays() const {
 }
 
 std::vector<gfx::Display> ScreenWin::GetAllDisplays() const {
-  std::vector<gfx::Display> all_displays;
-  EnumDisplayMonitors(NULL, NULL, EnumMonitorCallback,
-                      reinterpret_cast<LPARAM>(&all_displays));
-  return all_displays;
+  return displays_;
 }
 
 gfx::Display ScreenWin::GetDisplayNearestWindow(gfx::NativeView window) const {
@@ -166,11 +167,11 @@ gfx::Display ScreenWin::GetPrimaryDisplay() const {
 }
 
 void ScreenWin::AddObserver(DisplayObserver* observer) {
-  // TODO(oshima): crbug.com/122863.
+  change_notifier_.AddObserver(observer);
 }
 
 void ScreenWin::RemoveObserver(DisplayObserver* observer) {
-  // TODO(oshima): crbug.com/122863.
+  change_notifier_.RemoveObserver(observer);
 }
 
 HWND ScreenWin::GetHWNDFromNativeView(NativeView window) const {
@@ -183,4 +184,37 @@ NativeWindow ScreenWin::GetNativeWindowFromHWND(HWND hwnd) const {
   return NULL;
 }
 
+std::vector<gfx::Display> ScreenWin::BuildDisplays() const {
+  std::vector<gfx::Display> all_displays;
+  EnumDisplayMonitors(NULL, NULL, EnumMonitorCallback,
+                      reinterpret_cast<LPARAM>(&all_displays));
+  return all_displays;
+}
+
+void ScreenWin::OnDisplayChanged() {
+  // Windows send a WM_DISPLAYCHANGE message to all windows when the displays
+  // change. This method will be called when this happen. In order to prevent
+  // doing expensive work multiple time, we use a timer that will be reset
+  // every time we get a new call and will be fulfilled kConfigureDelayMs after
+  // the latest.
+  if (configure_timer_.get() && configure_timer_->IsRunning()) {
+    configure_timer_->Reset();
+    return;
+  }
+
+  configure_timer_.reset(new base::OneShotTimer<ScreenWin>());
+  configure_timer_->Start(
+      FROM_HERE,
+      base::TimeDelta::FromMilliseconds(kConfigureDelayMs),
+      this,
+      &ScreenWin::ConfigureTimerFired);
+}
+
+void ScreenWin::ConfigureTimerFired() {
+  std::vector<gfx::Display> old_displays = displays_;
+  displays_ = BuildDisplays();
+
+  change_notifier_.NotifyDisplaysChanged(old_displays, displays_);
+}
+
 }  // namespace gfx