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

components/tracing/trace_config_file.cc

Index: components/tracing/trace_config_file.cc
diff --git a/components/tracing/trace_config_file.cc b/components/tracing/trace_config_file.cc
index 670bcc9c2064d52257d973c4d7a1a9878812d85b..56e3ea5cf2bcdf429fbfb0eef011b2c6a9526576 100644
--- a/components/tracing/trace_config_file.cc
+++ b/components/tracing/trace_config_file.cc
@@ -11,7 +11,6 @@
 #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"
@@ -108,9 +107,7 @@ bool TraceConfigFile::ParseTraceConfigFileContent(const std::string& content) {
   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);
+  trace_config_ = base::trace_event::TraceConfig(*trace_config_dict);
 
   if (!dict->GetInteger(kStartupDurationParam, &startup_duration_))
       startup_duration_ = 0;