[DevTools] Add implementation for Tracing.start with optional parameters.

content/browser/devtools/protocol/tracing_handler.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 "content/browser/devtools/protocol/tracing_handler.h"
 
 namespace content {
 namespace devtools {
 namespace tracing {
 
 typedef DevToolsProtocolClient::Response Response;
 
 TracingHandler::TracingHandler() {
 }
 
 TracingHandler::~TracingHandler() {
 }
 
 void TracingHandler::SetClient(scoped_ptr<Client> client) {
   client_.swap(client);
 }
 
-Response TracingHandler::Start(const std::string& categories,
-                               const std::string& options,
-                               const double* buffer_usage_reporting_interval) {
-  return Response::FallThrough();
-}
-
 scoped_refptr<DevToolsProtocol::Response> TracingHandler::Start(
     const std::string& categories,
     const std::string& options,
     const double* buffer_usage_reporting_interval,
     scoped_refptr<DevToolsProtocol::Command> command) {
   return NULL;
 }
 
-Response TracingHandler::End() {
-  return Response::FallThrough();
+scoped_refptr<DevToolsProtocol::Response> TracingHandler::Start(
+    const std::string* categories,
+    const std::string* options,
+    const double* buffer_usage_reporting_interval,
+    scoped_refptr<DevToolsProtocol::Command> command) {
+  return NULL;
 }
 
 scoped_refptr<DevToolsProtocol::Response> TracingHandler::End(
     scoped_refptr<DevToolsProtocol::Command> command) {
   return NULL;
 }
 
 scoped_refptr<DevToolsProtocol::Response> TracingHandler::GetCategories(
     scoped_refptr<DevToolsProtocol::Command> command) {
   return NULL;
 }
 
 }  // namespace tracing
 }  // namespace devtools
 }  // namespace content