[inspector_protocol] support fall through and moveable Maybe

inspector_protocol.gni

 # 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.
 
 # This template will generate inspector protocol source code. The code will
 # not be compiled, use get_target_outputs(<name>) to compile them.
 #
 # Inputs
 #
 #   config_file  (required)
@@ skipping 15 matching lines @@
   assert(defined(invoker.inspector_protocol_dir))
   inspector_protocol_dir = invoker.inspector_protocol_dir
 
   action(target_name) {
     script = "$inspector_protocol_dir/CodeGenerator.py"
 
     inputs = [
       invoker.config_file,
       "$inspector_protocol_dir/lib/Allocator_h.template",
       "$inspector_protocol_dir/lib/Array_h.template",
-      "$inspector_protocol_dir/lib/BackendCallback_h.template",
       "$inspector_protocol_dir/lib/Collections_h.template",
       "$inspector_protocol_dir/lib/DispatcherBase_cpp.template",
       "$inspector_protocol_dir/lib/DispatcherBase_h.template",
       "$inspector_protocol_dir/lib/ErrorSupport_cpp.template",
       "$inspector_protocol_dir/lib/ErrorSupport_h.template",
       "$inspector_protocol_dir/lib/Forward_h.template",
       "$inspector_protocol_dir/lib/FrontendChannel_h.template",
       "$inspector_protocol_dir/lib/Maybe_h.template",
       "$inspector_protocol_dir/lib/Object_cpp.template",
       "$inspector_protocol_dir/lib/Object_h.template",
@@ skipping 25 matching lines @@
                             "abspath")
 
     forward_variables_from(invoker,
                            [
                              "visibility",
                              "deps",
                              "public_deps",
                            ])
   }
 }