Use a mocked compositor for unit tests

ui/gfx/compositor/compositor.h

 // Copyright (c) 2011 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_GFX_COMPOSITOR_COMPOSITOR_H_
 #define UI_GFX_COMPOSITOR_COMPOSITOR_H_
 #pragma once
 
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
@@ skipping 119 matching lines @@
 
   // Returns the size of the widget that is being drawn to.
   const gfx::Size& size() { return size_; }
 
   // Compositor does not own observers. It is the responsibility of the
   // observer to remove itself when it is done observing.
   void AddObserver(CompositorObserver* observer);
   void RemoveObserver(CompositorObserver* observer);
   bool HasObserver(CompositorObserver* observer);
 
+  static void set_compositor_factory_for_testing(
+      ui::Compositor*(*factory)(ui::CompositorDelegate* owner)) {
+    compositor_factory_ = factory;
+  }
+
+  static ui::Compositor* (*compositor_factory())(
+      ui::CompositorDelegate* owner) {
+    return compositor_factory_;
+  }
+
  protected:
   Compositor(CompositorDelegate* delegate, const gfx::Size& size);
   virtual ~Compositor();
 
   // Notifies the compositor that compositing is about to start.
   virtual void OnNotifyStart(bool clear) = 0;
 
   // Notifies the compositor that compositing is complete.
   virtual void OnNotifyEnd() = 0;
 
@@ skipping 12 matching lines @@
   void NotifyEnd();
 
   CompositorDelegate* delegate_;
   gfx::Size size_;
 
   // The root of the Layer tree drawn by this compositor.
   Layer* root_layer_;
 
   ObserverList<CompositorObserver> observer_list_;
 
+  // Factory used to create Compositors. Settable by tests.
+  // The delegate can be NULL if you don't wish to catch the ScheduleDraw()
+  // calls to it.
+  static ui::Compositor*(*compositor_factory_)(
+      ui::CompositorDelegate* delegate);
+
   friend class base::RefCounted<Compositor>;
 };
 
 }  // namespace ui
 
 #endif  // UI_GFX_COMPOSITOR_COMPOSITOR_H_