[inspector] use own copy of third_party/inspector_protocol

src/inspector/BUILD.gn

 # Copyright 2016 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("../../gni/v8.gni")
 
-_inspector_protocol = "//third_party/WebKit/Source/platform/inspector_protocol"
+_inspector_protocol = v8_path_prefix + "/third_party/inspector_protocol"
 import("$_inspector_protocol/inspector_protocol.gni")
 
 _protocol_generated = [
   "protocol/Forward.h",
   "protocol/Protocol.cpp",
   "protocol/Protocol.h",
   "protocol/Console.cpp",
   "protocol/Console.h",
   "protocol/Debugger.cpp",
   "protocol/Debugger.h",
@@ skipping 26 matching lines @@
     rebase_path("js_protocol.json", root_build_dir),
   ]
 }
 
 inspector_protocol_generate("protocol_generated_sources") {
   visibility = [ ":*" ]  # Only targets in this file can depend on this.
   deps = [
     ":protocol_compatibility",
   ]
 
+  inspector_protocol_dir = _inspector_protocol
   out_dir = target_gen_dir
   config_file = "inspector_protocol_config.json"
   inputs = [
     "js_protocol.json",
     "inspector_protocol_config.json",
   ]
   outputs = _protocol_generated
 }
 
 action("inspector_injected_script") {
@@ skipping 116 matching lines @@
     "v8-runtime-agent-impl.cc",
     "v8-runtime-agent-impl.h",
     "v8-schema-agent-impl.cc",
     "v8-schema-agent-impl.h",
     "v8-stack-trace-impl.cc",
     "v8-stack-trace-impl.h",
     "v8-value-copier.cc",
     "v8-value-copier.h",
   ]
 }