DevTools: update transfer mode in Tracing.start when using start-up tracing

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"
 
 #include <cmath>
 
 #include "base/bind.h"
 #include "base/format_macros.h"
@@ skipping 161 matching lines @@
       TracingCompleteParams::Create()->set_stream(stream_handle));
 }
 
 Response TracingHandler::Start(
     DevToolsCommandId command_id,
     const std::string* categories,
     const std::string* options,
     const double* buffer_usage_reporting_interval,
     const std::string* transfer_mode,
     const std::unique_ptr<base::DictionaryValue>& config) {
-  if (IsTracing())
+  if (IsTracing()) {
+    if (!did_initiate_recording_ && IsStartupTracingActive()) {
+      // If tracing is already running because it was initiated by startup
+      // tracing, honor the transfer mode update, as that's the only way
+      // for the client to communicate it.
+      return_as_stream_ =
+          transfer_mode && *transfer_mode == start::kTransferModeReturnAsStream;
+    }
     return Response::InternalError("Tracing is already started");
+  }
 
   if (config && (categories || options)) {
     return Response::InternalError(
         "Either trace config (preferred), or categories+options should be "
         "specified, but not both.");
   }
 
   did_initiate_recording_ = true;
   return_as_stream_ =
       transfer_mode && *transfer_mode == start::kTransferModeReturnAsStream;
@@ skipping 154 matching lines @@
   std::string mode;
   if (tracing_dict->GetString(kRecordModeParam, &mode))
     tracing_dict->SetString(kRecordModeParam, ConvertFromCamelCase(mode, '-'));
 
   return base::trace_event::TraceConfig(*tracing_dict);
 }
 
 }  // namespace tracing
 }  // namespace devtools
 }  // namespace content