Add flag to launch two displays for mus+ash.

services/ui/ws/frame_generator.cc

 // Copyright 2016 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 "services/ui/ws/frame_generator.h"
 
 #include "base/containers/adapters.h"
 #include "cc/output/compositor_frame.h"
 #include "cc/quads/render_pass.h"
 #include "cc/quads/render_pass_draw_quad.h"
@@ skipping 75 matching lines @@
 void FrameGenerator::DidDraw() {
   frame_pending_ = false;
   delegate_->OnCompositorFrameDrawn();
   if (!dirty_rect_.IsEmpty())
     WantToDraw();
 }
 
 cc::CompositorFrame FrameGenerator::GenerateCompositorFrame() {
   const ViewportMetrics& metrics = delegate_->GetViewportMetrics();
   std::unique_ptr<cc::RenderPass> render_pass = cc::RenderPass::Create();
-  gfx::Rect output_rect(metrics.size_in_pixels);
+  gfx::Rect output_rect = metrics.bounds;
   dirty_rect_.Intersect(output_rect);
   const cc::RenderPassId render_pass_id(1, 1);
   render_pass->SetNew(render_pass_id, output_rect, dirty_rect_,
                       gfx::Transform());
 
   DrawWindowTree(render_pass.get(), delegate_->GetRootWindow(), gfx::Vector2d(),
                  1.0f);
 
   std::unique_ptr<cc::DelegatedFrameData> frame_data(
       new cc::DelegatedFrameData);
@@ skipping 93 matching lines @@
     quad->SetAll(sqs, bounds_at_origin /* rect */,
                  gfx::Rect() /* opaque_rect */,
                  bounds_at_origin /* visible_rect */, true /* needs_blending*/,
                  underlay_surface->id());
   }
 }
 
 }  // namespace ws
 
 }  // namespace ui