Created uber tray UI for monitoring ongoing WebDrive sync operations

ash/system/tray/system_tray.h

Index: ash/system/tray/system_tray.h
diff --git a/ash/system/tray/system_tray.h b/ash/system/tray/system_tray.h
index 8bb6559304934e5f4cb0de94a3b3e9648960ee9d..7280c90f19d0619d6355011aeae8abaad3b8b45e 100644
--- a/ash/system/tray/system_tray.h
+++ b/ash/system/tray/system_tray.h
@@ -27,6 +27,7 @@ class BluetoothObserver;
 class BrightnessObserver;
 class CapsLockObserver;
 class ClockObserver;
+class DriveObserver;
 class IMEObserver;
 class NetworkObserver;
 class PowerStatusObserver;
@@ -108,6 +109,9 @@ class ASH_EXPORT SystemTray : NON_EXPORTED_BASE(
   ClockObserver* clock_observer() const {
     return clock_observer_;
   }
+  DriveObserver* drive_observer() const {
+    return drive_observer_;
+  }
   IMEObserver* ime_observer() const {
     return ime_observer_;
   }
@@ -164,6 +168,7 @@ class ASH_EXPORT SystemTray : NON_EXPORTED_BASE(
   BrightnessObserver* brightness_observer_;
   CapsLockObserver* caps_lock_observer_;
   ClockObserver* clock_observer_;
+  DriveObserver* drive_observer_;
   IMEObserver* ime_observer_;
   NetworkObserver* network_observer_;
   PowerStatusObserver* power_status_observer_;