Revert r267126: "DevTools: handle Tracing.start in both browser and renderer" It was plain wrong.

TBR=caseq,yurys
BUG=374411

Review URL: https://codereview.chromium.org/288423004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@271296 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/devtools/devtools_tracing_handler.cc

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

content/browser/devtools/devtools_tracing_handler.h

@@ -27,6 +27,7 @@ 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(