a11y: announce hold-to-quit message

Since the hold-to-quit message is delivered by a borderless window,
VoiceOver does not announce its presence; we need to explicitly announce
its message here so screenreader users know why their quit command is
not immediate.

Bug: 957356
Change-Id: I7df32194175decffe8f97a02644d5b7dfc9aba0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1606380
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Auto-Submit: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659044}

chrome/browser/ui/cocoa/confirm_quit_panel_controller.mm

@@ -154,6 +154,7 @@ const NSTimeInterval kTimeDeltaFuzzFactor = 1.0;
 // Returns the menu item for the Quit menu item, or a thrown-together default
 // one if no Quit menu item exists.
 + (NSMenuItem*)quitMenuItem;
+- (void)sendAccessibilityAnnouncement;
 @end
 
 ConfirmQuitPanelController* g_confirmQuitPanelController = nil;
@@ -236,6 +237,13 @@ ConfirmQuitPanelController* g_confirmQuitPanelController = nil;
   // Show the info panel that explains what the user must to do confirm quit.
   [self showWindow:self];
 
+  // Explicitly announce the hold-to-quit message. For an ordinary modal dialog
+  // VoiceOver would announce it and read its message, but VoiceOver does not do
+  // this for windows whose styleMask is NSBorderlessWindowMask, so do it
+  // manually here. Without this screenreader users have no way to know why
+  // their quit hotkey seems not to work.
+  [self sendAccessibilityAnnouncement];
+
   // Spin a nested run loop until the |targetDate| is reached or a KeyUp event
   // is sent.
   NSDate* targetDate = [NSDate
@@ -396,4 +404,16 @@ ConfirmQuitPanelController* g_confirmQuitPanelController = nil;
   return string;
 }
 
+- (void)sendAccessibilityAnnouncement {
+  NSString* message = l10n_util::GetNSStringF(
+      IDS_CONFIRM_TO_QUIT_DESCRIPTION,
+      base::SysNSStringToUTF16([[self class] keyCommandString]));
+
+  NSAccessibilityPostNotificationWithUserInfo(
+      [NSApp mainWindow], NSAccessibilityAnnouncementRequestedNotification, @{
+        NSAccessibilityAnnouncementKey : message,
+        NSAccessibilityPriorityKey : @(NSAccessibilityPriorityHigh),
+      });
+}
+
 @end