[MacViews] Implement ChromeNativeAppWindowViewsMac::FlashFrame.

Same as NativeAppWindowCocoa. This behavior is only for app windows.

BUG=459877

Review URL: https://codereview.chromium.org/1105663004

Cr-Commit-Position: refs/heads/master@{#327008}

chrome/browser/ui/views/apps/chrome_native_app_window_views_mac.h

@@ -24,6 +24,7 @@ class ChromeNativeAppWindowViewsMac : public ChromeNativeAppWindowViews {
   // ui::BaseWindow implementation.
   void Show() override;
   void ShowInactive() override;
+  void FlashFrame(bool flash) override;
 
   // NativeAppWindow implementation.
   // These are used to simulate Mac-style hide/show. Since windows can be hidden

chrome/browser/ui/views/apps/chrome_native_app_window_views_mac.mm

@@ -50,6 +50,12 @@ void ChromeNativeAppWindowViewsMac::ShowInactive() {
   ChromeNativeAppWindowViews::ShowInactive();
 }
 
+void ChromeNativeAppWindowViewsMac::FlashFrame(bool flash) {
+  apps::ExtensionAppShimHandler::RequestUserAttentionForWindow(
+      app_window(), flash ? apps::APP_SHIM_ATTENTION_CRITICAL
+                          : apps::APP_SHIM_ATTENTION_CANCEL);
+}
+
 void ChromeNativeAppWindowViewsMac::ShowWithApp() {
   is_hidden_with_app_ = false;
   if (!app_window()->is_hidden())