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 4ea3e63c70e25c5c3073e67ef1a5f59d942087d3..f608e70cef7f6c731167173312c347ca6e5ff0da 100644
--- a/ash/system/tray/system_tray.h
+++ b/ash/system/tray/system_tray.h
@@ -26,6 +26,7 @@ class BluetoothObserver;
 class BrightnessObserver;
 class CapsLockObserver;
 class ClockObserver;
+class DriveObserver;
 class IMEObserver;
 class NetworkObserver;
 class PowerStatusObserver;
@@ -105,6 +106,9 @@ 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_;
   }
@@ -160,6 +164,7 @@ 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_;