Close Views menus when switching apps.

BUG=988979
TEST=as in bug

Change-Id: I40c09d3f3d630d2ef4762d7970d6a6ec52a875ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1727489Reviewed-by: Leonard Grey <lgrey@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682725}

ui/views/controls/menu/menu_cocoa_watcher_mac.h

@@ -32,6 +32,7 @@ class VIEWS_EXPORT MenuCocoaWatcherMac {
   // Tokens representing the notification observers.
   id observer_token_other_menu_;
   id observer_token_new_window_focus_;
+  id observer_token_app_change_;
 
   DISALLOW_COPY_AND_ASSIGN(MenuCocoaWatcherMac);
 };

ui/views/controls/menu/menu_cocoa_watcher_mac.mm

@@ -27,6 +27,14 @@ MenuCocoaWatcherMac::MenuCocoaWatcherMac(base::OnceClosure callback)
               usingBlock:^(NSNotification* notification) {
                 ExecuteCallback();
               }];
+  observer_token_app_change_ =
+      [[[NSWorkspace sharedWorkspace] notificationCenter]
+          addObserverForName:NSWorkspaceDidActivateApplicationNotification
+                      object:nil
+                       queue:nil
+                  usingBlock:^(NSNotification* notification) {
+                    ExecuteCallback();
+                  }];
 }
 
 MenuCocoaWatcherMac::~MenuCocoaWatcherMac() {
@@ -34,6 +42,8 @@ MenuCocoaWatcherMac::~MenuCocoaWatcherMac() {
       removeObserver:observer_token_other_menu_];
   [[NSNotificationCenter defaultCenter]
       removeObserver:observer_token_new_window_focus_];
+  [[[NSWorkspace sharedWorkspace] notificationCenter]
+      removeObserver:observer_token_app_change_];
 }
 
 void MenuCocoaWatcherMac::ExecuteCallback() {