Add UI for cast system tray integration

ash/system/chromeos/screen_security/screen_capture_tray_item.cc

Index: ash/system/chromeos/screen_security/screen_capture_tray_item.cc
diff --git a/ash/system/chromeos/screen_security/screen_capture_tray_item.cc b/ash/system/chromeos/screen_security/screen_capture_tray_item.cc
index c4689ded2cac3c6cb62486c8d7eb69d46ab1872f..c8c5bac2ac198db76e376bc3a995060174d20c1c 100644
--- a/ash/system/chromeos/screen_security/screen_capture_tray_item.cc
+++ b/ash/system/chromeos/screen_security/screen_capture_tray_item.cc
@@ -24,11 +24,13 @@ const char kScreenCaptureNotificationId[] = "chrome://screen/capture";
 
 ScreenCaptureTrayItem::ScreenCaptureTrayItem(SystemTray* system_tray)
     : ScreenTrayItem(system_tray) {
+  Shell::GetInstance()->AddShellObserver(this);
   Shell::GetInstance()->system_tray_notifier()->
       AddScreenCaptureObserver(this);
 }
 
 ScreenCaptureTrayItem::~ScreenCaptureTrayItem() {
+  Shell::GetInstance()->RemoveShellObserver(this);
   Shell::GetInstance()->system_tray_notifier()->
       RemoveScreenCaptureObserver(this);
 }
@@ -79,6 +81,17 @@ void ScreenCaptureTrayItem::OnScreenCaptureStart(
     const base::Closure& stop_callback,
     const base::string16& screen_capture_status) {
   screen_capture_status_ = screen_capture_status;
+
+  // This suppression technique is currently dependent on the order
+  // that OnScreenCaptureStart and OnCastingSessionStartedOrStopped
+  // get invoked. OnCastingSessionStartedOrStopped currently gets
+  // called first.
+  //
+  // TODO(jdufault): Does this break casting and capturing the screen at the
+  //                 same time?
+  if (is_casting_)
+    return;
+
   Start(stop_callback);
 }
 
@@ -89,4 +102,8 @@ void ScreenCaptureTrayItem::OnScreenCaptureStop() {
   Update();
 }
 
+void ScreenCaptureTrayItem::OnCastingSessionStartedOrStopped(bool started) {
+  is_casting_ = started;
+}
+
 }  // namespace ash