Change OnWindowInputEvent to use display_id to find the host and update event root_location in WS.

services/ui/ws/window_tree.cc

 // Copyright 2014 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_tree.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 139 matching lines @@
     return false;
   if (id)
     *id = iter->second;
   return true;
 }
 
 bool WindowTree::HasRoot(const ServerWindow* window) const {
   return roots_.count(window) > 0;
 }
 
+const ServerWindow* WindowTree::FindRootFor(const ServerWindow* window) const {
+  for (const ServerWindow* parent = window; parent; parent = parent->parent()) {
+    if (roots_.count(parent))
+      return parent;
+  }
+  return nullptr;
+}
+
 const ServerWindow* WindowTree::GetWindowByClientId(
     const ClientWindowId& id) const {
   auto iter = client_id_to_window_id_map_.find(id);
   return iter == client_id_to_window_id_map_.end() ? nullptr
                                                    : GetWindow(iter->second);
 }
 
 const Display* WindowTree::GetDisplay(const ServerWindow* window) const {
   return window ? display_manager()->GetDisplayContaining(window) : nullptr;
 }
@@ skipping 2009 matching lines @@
   client()->OnCompleteDrop(client_window_id.id, event_flags, cursor_offset,
                            effect_bitmask, callback);
 }
 
 void WindowTree::PerformOnDragDropDone() {
   client()->OnDragDropDone();
 }
 
 }  // namespace ws
 }  // namespace ui