Support a ui::test::EventGenerator constructed with a single argument on Mac

ui/events/test/event_generator.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_EVENTS_TEST_EVENT_GENERATOR_H_
 #define UI_EVENTS_TEST_EVENT_GENERATOR_H_
 
 #include <list>
 #include <memory>
 #include <vector>
@@ skipping 104 matching lines @@
   // which uses the coordinates conversions and targeting provided by
   // |delegate|.
   explicit EventGenerator(EventGeneratorDelegate* delegate);
 
   // Creates an EventGenerator with the mouse/touch location
   // at |initial_location|, which uses the |root_window|'s coordinates.
   EventGenerator(gfx::NativeWindow root_window,
                  const gfx::Point& initial_location);
 
   // Creates an EventGenerator with the mouse/touch location centered over
-  // |window|. This is currently the only constructor that works on Mac, since
-  // a specific window is required (and there is no root window).
+  // |window|.
   EventGenerator(gfx::NativeWindow root_window, gfx::NativeWindow window);
 
   virtual ~EventGenerator();
 
   // Explicitly sets the location used by mouse/touch events. This is set by the
   // various methods that take a location but can be manipulated directly,
   // typically for touch.
   void set_current_location(const gfx::Point& location) {
     current_location_ = location;
   }
@@ skipping 271 matching lines @@
   bool targeting_application_;
   std::unique_ptr<base::TickClock> tick_clock_;
 
   DISALLOW_COPY_AND_ASSIGN(EventGenerator);
 };
 
 }  // namespace test
 }  // namespace ui
 
 #endif  // UI_EVENTS_TEST_EVENT_GENERATOR_H_