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

content/browser/devtools/devtools_tracing_handler.cc

Index: content/browser/devtools/devtools_tracing_handler.cc
diff --git a/content/browser/devtools/devtools_tracing_handler.cc b/content/browser/devtools/devtools_tracing_handler.cc
index 977f88e6945386aa41c496b582a7a84e7f569a9d..5e97b1b69343cf4c83967507b6d678948869ea64 100644
--- a/content/browser/devtools/devtools_tracing_handler.cc
+++ b/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) {