aura: changes EventInjector to query WindowTreeHost for display

Previously the code queried TestScreen. This is problematic as
content_browsertests uses TestScreen, which *always* returns a display
id of 2000. When mus gets the event the event is then dropped (because
it doesn't know about 2000). This changes EventInjector to query
WindowTreeHost and has WindowTreeHostMus override GetDisplayId() to
return the real display id.

BUG=786453
TEST=none

Change-Id: I01b9ce9096a0a3e7d6ca9cf85706afb0213035a7
Reviewed-on: https://chromium-review.googlesource.com/809493Reviewed-by: Elliot Glaysher <erg@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521813}

ui/aura/event_injector.cc

@@ -9,8 +9,6 @@
 #include "ui/aura/env.h"
 #include "ui/aura/mus/window_tree_client.h"
 #include "ui/aura/window_tree_host.h"
-#include "ui/display/display.h"
-#include "ui/display/screen.h"
 #include "ui/events/event.h"
 #include "ui/events/event_sink.h"
 
@@ -51,9 +49,8 @@ ui::EventDispatchDetails EventInjector::Inject(WindowTreeHost* host,
     env->window_tree_client_->connector()->BindInterface(
         ui::mojom::kServiceName, &window_server_ptr_);
   }
-  display::Screen* screen = display::Screen::GetScreen();
   window_server_ptr_->DispatchEvent(
-      screen->GetDisplayNearestWindow(host->window()).id(), MapEvent(*event),
+      host->GetDisplayId(), MapEvent(*event),
       base::Bind([](bool result) { DCHECK(result); }));
   return ui::EventDispatchDetails();
 }

ui/aura/mus/window_tree_host_mus.cc

@@ -244,4 +244,8 @@ gfx::Transform WindowTreeHostMus::GetRootTransformForLocalEventCoordinates()
   return transform;
 }
 
+int64_t WindowTreeHostMus::GetDisplayId() {
+  return display_id_;
+}
+
 }  // namespace aura

ui/aura/mus/window_tree_host_mus.h

@@ -109,6 +109,7 @@ class AURA_EXPORT WindowTreeHostMus : public WindowTreeHostPlatform {
   void MoveCursorToScreenLocationInPixels(
       const gfx::Point& location_in_pixels) override;
   gfx::Transform GetRootTransformForLocalEventCoordinates() const override;
+  int64_t GetDisplayId() override;
 
  private:
   int64_t display_id_;

ui/aura/window_tree_host.cc

@@ -222,6 +222,10 @@ ui::EventDispatchDetails WindowTreeHost::DispatchKeyEventPostIME(
   return dispatch_details;
 }
 
+int64_t WindowTreeHost::GetDisplayId() {
+  return display::Screen::GetScreen()->GetDisplayNearestWindow(window()).id();
+}
+
 void WindowTreeHost::Show() {
   // Ensure that compositor has been properly initialized, see InitCompositor()
   // and InitHost().

ui/aura/window_tree_host.h

@@ -5,6 +5,8 @@
 #ifndef UI_AURA_WINDOW_TREE_HOST_H_
 #define UI_AURA_WINDOW_TREE_HOST_H_
 
+#include <stdint.h>
+
 #include <memory>
 #include <vector>
 
@@ -169,6 +171,9 @@ class AURA_EXPORT WindowTreeHost : public ui::internal::InputMethodDelegate,
   // Overridden from ui::internal::InputMethodDelegate:
   ui::EventDispatchDetails DispatchKeyEventPostIME(ui::KeyEvent* event) final;
 
+  // Returns the id of the display. Default implementation queries Screen.
+  virtual int64_t GetDisplayId();
+
   // Returns the EventSource responsible for dispatching events to the window
   // tree.
   virtual ui::EventSource* GetEventSource() = 0;