Revert of Makes change_id unsigned

mojo/examples/sample_view_manager_app/sample_view_manager_app.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 "base/bind.h"
 #include "mojo/public/cpp/bindings/allocation_scope.h"
 #include "mojo/public/cpp/bindings/remote_ptr.h"
 #include "mojo/public/cpp/environment/environment.h"
 #include "mojo/public/cpp/shell/application.h"
 #include "mojo/public/cpp/system/core.h"
@@ skipping 31 matching lines @@
 
   virtual ~SampleApp() {
   }
 
   // ViewManagerClient::
   virtual void OnConnectionEstablished(uint16_t connection_id) OVERRIDE {
   }
   virtual void OnNodeHierarchyChanged(uint32_t node,
                                       uint32_t new_parent,
                                       uint32_t old_parent,
-                                      uint32_t change_id) OVERRIDE {
+                                      int32_t change_id) OVERRIDE {
   }
   virtual void OnNodeViewReplaced(uint32_t node,
                                   uint32_t old_view_id,
                                   uint32_t new_view_id,
-                                  uint32_t change_id) OVERRIDE {
+                                  int32_t change_id) OVERRIDE {
   }
 
  private:
   void OnCreatedView(bool success) {
     DCHECK(success);
   }
 
   RemotePtr<services::view_manager::ViewManager> view_manager_;
 };
 
 }  // namespace examples
 }  // namespace mojo
 
 extern "C" SAMPLE_APP_EXPORT MojoResult CDECL MojoMain(
     MojoHandle shell_handle) {
   mojo::Environment env;
   mojo::RunLoop loop;
 
   mojo::examples::SampleApp app(shell_handle);
   loop.Run();
   return MOJO_RESULT_OK;
 }