[Mac][MC] Close the tray window when the user clicks outside it.

ui/message_center/cocoa/tray_controller.mm

Index: ui/message_center/cocoa/tray_controller.mm
diff --git a/ui/message_center/cocoa/tray_controller.mm b/ui/message_center/cocoa/tray_controller.mm
index 6b78d657231254c3835bb2226b740c000c4130be..abe07e3aff0934d4d5b35adebde4dc60fa151c3c 100644
--- a/ui/message_center/cocoa/tray_controller.mm
+++ b/ui/message_center/cocoa/tray_controller.mm
@@ -43,10 +43,26 @@
     NSView* contentView = [viewController_ view];
     [window setFrame:[contentView frame] display:NO];
     [window setContentView:contentView];
+
+    // The global event monitor will close the tray in response to events
+    // delivered to other applications, and -windowDidResignKey: will catch
+    // events within the application.
+    clickEventMonitor_ =
+        [NSEvent addGlobalMonitorForEventsMatchingMask:NSLeftMouseDownMask |
+                                                       NSRightMouseDownMask |
+                                                       NSOtherMouseDownMask
+            handler:^(NSEvent* event) {
+                tray_->HideMessageCenterBubble();
+            }];
   }
   return self;
 }
 
+- (void)dealloc {
+  [NSEvent removeMonitor:clickEventMonitor_];
+  [super dealloc];
+}
+
 - (void)showTrayAt:(NSPoint)point {
   NSRect frame = [[viewController_ view] frame];
   frame.origin.x = point.x;