Implement a "continue-activity" event on app for resuming from hand-off.

atom/browser/browser.cc

@@ -137,6 +137,17 @@ void Browser::Activate(bool has_visible_windows) {
                     OnActivate(has_visible_windows));
 }
 
+#if defined(OS_MACOSX)
+bool Browser::ContinueUserActivity(const std::string& type, const std::map<std::string, std::string>& user_info) {
+  bool handled = false;
+  FOR_EACH_OBSERVER(BrowserObserver, 
+                    observers_, 
+                    OnContinueUserActivity(&handled, type, user_info));
+                    
+  return handled;
+}
+#endif
+
 void Browser::WillFinishLaunching() {
   FOR_EACH_OBSERVER(BrowserObserver, observers_, OnWillFinishLaunching());
 }