Update DevTools Tracing.Start to accept trace config as a parameter

components/tracing/trace_config_file.cc

 // Copyright (c) 2015 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 "components/tracing/trace_config_file.h"
 
 #include <stddef.h>
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/json/json_reader.h"
-#include "base/json/json_writer.h"
 #include "base/logging.h"
 #include "base/memory/singleton.h"
 #include "base/values.h"
 #include "build/build_config.h"
 #include "components/tracing/tracing_switches.h"
 
 namespace tracing {
 
 namespace {
 
@@ skipping 76 matching lines @@
   if (!value || !value->IsType(base::Value::TYPE_DICTIONARY))
     return false;
 
   scoped_ptr<base::DictionaryValue> dict(
       static_cast<base::DictionaryValue*>(value.release()));
 
   base::DictionaryValue* trace_config_dict = NULL;
   if (!dict->GetDictionary(kTraceConfigParam, &trace_config_dict))
     return false;
 
-  std::string trace_config_str;
-  base::JSONWriter::Write(*trace_config_dict, &trace_config_str);
-  trace_config_ = base::trace_event::TraceConfig(trace_config_str);
+  DCHECK(trace_config_dict);

[Primiano Tucci (use gerrit), 2016/03/15 12:22:41]

If you dereference a ptr there is no point adding a DCHECK, your code will crash
on the next line anyways, DCHECK does not add anything useful.
It's different if you were storing a pointer and reusing it later.

[Zhen Wang, 2016/03/15 16:53:55]

I see. removed. 

+  trace_config_ = base::trace_event::TraceConfig(*trace_config_dict);
 
   if (!dict->GetInteger(kStartupDurationParam, &startup_duration_))
       startup_duration_ = 0;
 
   if (startup_duration_ < 0)
       startup_duration_ = 0;
 
   base::FilePath::StringType result_file_str;
   if (dict->GetString(kResultFileParam, &result_file_str))
     result_file_ = base::FilePath(result_file_str);
@@ skipping 16 matching lines @@
 }
 
 #if !defined(OS_ANDROID)
 base::FilePath TraceConfigFile::GetResultFile() const {
   DCHECK(IsEnabled());
   return result_file_;
 }
 #endif
 
 }  // namespace tracing