DevTools: handle Tracing.start in both browser and renderer

Do not return response from browser override for Tracing.start, so
we invoke one in the renderer.
For blink counterpart, see: https://codereview.chromium.org/254613002

BUG=361045

Review URL: https://codereview.chromium.org/256473004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@267126 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/devtools/devtools_tracing_handler.cc

@@ -169,17 +169,9 @@ DevToolsTracingHandler::OnStart(
   }
 
   TracingController::GetInstance()->EnableRecording(
-      categories, options,
-      base::Bind(&DevToolsTracingHandler::OnTracingStarted,
-                 weak_factory_.GetWeakPtr(),
-                 command));
+      categories, options, TracingController::EnableRecordingDoneCallback());
 
-  return command->AsyncResponsePromise();
-}
-
-void DevToolsTracingHandler::OnTracingStarted(
-    scoped_refptr<DevToolsProtocol::Command> command) {
-  SendAsyncResponse(command->SuccessResponse(NULL));
+  return NULL;
 }
 
 void DevToolsTracingHandler::OnBufferUsage(float usage) {

content/browser/devtools/devtools_tracing_handler.h

@@ -27,7 +27,6 @@ class DevToolsTracingHandler : public DevToolsProtocol::Handler {
   void BeginReadingRecordingResult(const base::FilePath& path);
   void ReadRecordingResult(const scoped_refptr<base::RefCountedString>& result);
   void OnTraceDataCollected(const std::string& trace_fragment);
-  void OnTracingStarted(scoped_refptr<DevToolsProtocol::Command> command);
   void OnBufferUsage(float usage);
 
   scoped_refptr<DevToolsProtocol::Response> OnStart(