aura-mus: create an interactive ui test for drag and drop.

services/ui/ws/window_server_test_impl.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/window_server_test_impl.h"
 
 #include "services/ui/public/interfaces/window_tree.mojom.h"
+#include "services/ui/ws/display.h"
+#include "services/ui/ws/display_manager.h"
 #include "services/ui/ws/server_window.h"
 #include "services/ui/ws/server_window_compositor_frame_sink_manager.h"
 #include "services/ui/ws/window_server.h"
 #include "services/ui/ws/window_tree.h"
 
 namespace ui {
 namespace ws {
 
 WindowServerTestImpl::WindowServerTestImpl(WindowServer* window_server)
     : window_server_(window_server) {}
@@ skipping 24 matching lines @@
         return;
       }
     }
   }
 
   window_server_->SetPaintCallback(
       base::Bind(&WindowServerTestImpl::OnWindowPaint, base::Unretained(this),
                  client_name, std::move(callback)));
 }
 
+void WindowServerTestImpl::DispatchEvent(int64_t display_id,
+                                         std::unique_ptr<ui::Event> event,
+                                         const DispatchEventCallback& cb) {
+  DisplayManager* manager = window_server_->display_manager();
+  if (!manager) {
+    DVLOG(1) << "No display manager in DispatchEvent.";
+    cb.Run(false);
+    return;
+  }
+
+  Display* display = manager->GetDisplayById(display_id);
+  if (!display) {
+    DVLOG(1) << "Invalid display_id in DispatchEvent.";
+    cb.Run(false);
+    return;
+  }
+
+  if (!event) {

[sky, 2017/03/17 00:02:21]

Correct me if I'm wrong, but because the mojom doesn't declare the event as
optional I don't think event can be null, or at least I think there would be a
binding error if it is.

[Elliot Glaysher, 2017/03/17 17:43:11]

Done.

+    DVLOG(1) << "Passed null event in DispatchEvent.";
+    cb.Run(false);
+    return;
+  }
+
+  static_cast<PlatformDisplayDelegate*>(display)->OnEvent(*event.get());
+  cb.Run(true);
+}
+
 }  // namespace ws
 }  // namespace ui