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

BUG=405566
TBR=pfeldman

Review URL: https://codereview.chromium.org/663373002

Cr-Commit-Position: refs/heads/master@{#300477}

content/browser/devtools/protocol/tracing_handler.cc

@@ -20,12 +20,6 @@ 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,
@@ -34,8 +28,12 @@ scoped_refptr<DevToolsProtocol::Response> TracingHandler::Start(
   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(

content/browser/devtools/protocol/tracing_handler.h

@@ -20,18 +20,17 @@ class TracingHandler {
 
   void SetClient(scoped_ptr<Client> client);
 
-  // TODO(dgozman): remove sync version after migration.
-  Response Start(const std::string& categories,
-                 const std::string& options,
-                 const double* buffer_usage_reporting_interval);
   scoped_refptr<DevToolsProtocol::Response> Start(
       const std::string& categories,
       const std::string& options,
       const double* buffer_usage_reporting_interval,
       scoped_refptr<DevToolsProtocol::Command> command);
+  scoped_refptr<DevToolsProtocol::Response> Start(
+      const std::string* categories,
+      const std::string* options,
+      const double* buffer_usage_reporting_interval,
+      scoped_refptr<DevToolsProtocol::Command> command);
 
-  // TODO(dgozman): remove sync version after migration.
-  Response End();
   scoped_refptr<DevToolsProtocol::Response> End(
       scoped_refptr<DevToolsProtocol::Command> command);