views/mus: Install a mus-friend ContextFactory for tests.

ui/views/view_unittest.cc

 // Copyright (c) 2012 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.
 
 #include "ui/views/view.h"
 
 #include <stddef.h>
 
 #include <map>
 #include <memory>
@@ skipping 4189 matching lines @@
 
  private:
   bool painted_;
 
   DISALLOW_COPY_AND_ASSIGN(PaintTrackingView);
 };
 
 // Makes sure child views with layers aren't painted when paint starts at an
 // ancestor.
 TEST_F(ViewLayerTest, DontPaintChildrenWithLayers) {
-  // TODO(sad): DrawWaiterForTest does not work with mus. crbug.com/618136
-  if (IsMus())
-    return;
   PaintTrackingView* content_view = new PaintTrackingView;
   widget()->SetContentsView(content_view);
   content_view->SetPaintToLayer();
   GetRootLayer()->GetCompositor()->ScheduleDraw();
   ui::DrawWaiterForTest::WaitForCompositingEnded(
       GetRootLayer()->GetCompositor());
   GetRootLayer()->SchedulePaint(gfx::Rect(0, 0, 10, 10));
   content_view->set_painted(false);
   // content_view no longer has a dirty rect. Paint from the root and make sure
   // PaintTrackingView isn't painted.
@@ skipping 797 matching lines @@
   std::unique_ptr<View> view = NewView();
   std::unique_ptr<View> child_view = NewView();
   std::unique_ptr<View> child_view2 = NewView();
   view->AddChildView(child_view.get());
   view->AddChildView(child_view2.get());
   view->ReorderChildView(child_view2.get(), 0);
   EXPECT_EQ(child_view2.get(), view_reordered());
 }
 
 }  // namespace views