Expand Chrome OS ARC support to create one tree source per package

ui/accessibility/ax_host_delegate.h

 // Copyright 2017 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.
 
 #ifndef UI_ACCESSIBILITY_AX_HOST_DELEGATE_H_
 #define UI_ACCESSIBILITY_AX_HOST_DELEGATE_H_
 
 #include "ui/accessibility/ax_action_data.h"
 
 namespace ui {
@@ skipping 14 matching lines @@
  protected:
   // A delegate with an automatically assigned tree id.
   AXHostDelegate();
 
   // A delegate with an explicit tree id. The caller is responsible for ensuring
   // the uniqueness of the id.
   explicit AXHostDelegate(int32_t tree_id);
 
   // A tree id appropriate for annotating events sent to an accessibility
   // client.
-  int32_t tree_id() { return tree_id_; }
+  int32_t tree_id() const { return tree_id_; }
 
  private:
   // Register or unregister this class with |AXTreeIDRegistry|.
   void UpdateActiveState(bool active);
 
   int32_t tree_id_;
 };
 
 }  // namespace ui
 
 #endif  // UI_ACCESSIBILITY_AX_HOST_DELEGATE_H_