Handle modified displays in mustash.

ash/mus/window_manager.cc

Index: ash/mus/window_manager.cc
diff --git a/ash/mus/window_manager.cc b/ash/mus/window_manager.cc
index b72aa50567abffd463384d88d6714b256d5a3a2e..f86e19887346931debcb6ba91d1ca86a56ba5931 100644
--- a/ash/mus/window_manager.cc
+++ b/ash/mus/window_manager.cc
@@ -333,6 +333,19 @@ void WindowManager::OnWmDisplayRemoved(ui::Window* window) {
   DestroyRootWindowController(iter->get());
 }
 
+void WindowManager::OnWmDisplayModified(const display::Display& display) {
+  for (auto& controller : root_window_controllers_) {
+    if (controller->display().id() == display.id()) {
+      controller->set_display(display);

[sky, 2016/10/19 23:37:59]

Can you make set_display() call to UpdateDisplay()? Otherwise it's easy to miss
the call to UpdateDisplay, and it's wierd that this code updates the displaylist
but RootWindowController::SetWorkAreaInests does it as well.

[kylechar, 2016/10/20 15:04:19]

I could do that. In general it seems wrong to me that
RootWindowController::display_ exists in the first place. Screen has a copy of
Display and the two copes need to be identical. So it's twice the memory and
more code to keep them in sync.

It seems like lots of mash_unittests rely on RootWindowController::display_
existing though. So maybe I could remove it in a followup CL?

[sky, 2016/10/20 15:33:24]

Good point. I would still think RootWindowController should be the one updated
screen though as it does that in other places.

[kylechar, 2016/10/20 18:31:29]

Done.

+      screen_->display_list()->UpdateDisplay(display);
+      // The root window will be resized by the window server.
+      return;
+    }
+  }
+
+  NOTREACHED();
+}
+
 void WindowManager::OnWmPerformMoveLoop(
     ui::Window* window,
     ui::mojom::MoveLoopSource source,