Have Display root ServerWindow origin be (0, 0) for all displays.

services/ui/ws/frame_generator.cc

Index: services/ui/ws/frame_generator.cc
diff --git a/services/ui/ws/frame_generator.cc b/services/ui/ws/frame_generator.cc
index c944b651785d3ece393a03cb3dd884effdb0f68e..b46f17f6a6c2111c0b87c788748d3cf2ecfd9fc1 100644
--- a/services/ui/ws/frame_generator.cc
+++ b/services/ui/ws/frame_generator.cc
@@ -70,7 +70,7 @@ void FrameGenerator::Draw() {
     return;
 
   const ViewportMetrics& metrics = delegate_->GetViewportMetrics();
-  const gfx::Rect& output_rect = metrics.bounds;
+  const gfx::Rect output_rect(metrics.bounds.size());
   dirty_rect_.Intersect(output_rect);
   // TODO(fsamuel): We should add a trace for generating a top level frame.
   cc::CompositorFrame frame(GenerateCompositorFrame(output_rect));