Fix the output of chrome://slow so that is valid json

chrome/browser/feedback/tracing_manager.cc

 // Copyright 2013 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 "chrome/browser/feedback/tracing_manager.h"
 
 #include "base/bind.h"
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/feedback/feedback_util.h"
@@ skipping 75 matching lines @@
 void TracingManager::StartTracing() {
   content::TraceController::GetInstance()->BeginTracing(
       this, "-test_*",
       base::debug::TraceLog::RECORD_CONTINUOUSLY);
 }
 
 void TracingManager::OnEndTracingComplete() {
   if (!current_trace_id_)
     return;
 
+  data_ = std::string("[") + data_ + "]";
+
   std::string output_val;
   feedback_util::ZipString(data_, &output_val);
 
   scoped_refptr<base::RefCountedString> output(
       base::RefCountedString::TakeString(&output_val));
 
   trace_data_[current_trace_id_] = output;
 
   if (!trace_callback_.is_null()) {
     trace_callback_.Run(output);
     trace_callback_.Reset();
   }
 
   current_trace_id_ = 0;
   data_ = "";
 
   // Tracing has to be restarted asynchronous, so the TracingController can
   // clean up.
   base::MessageLoopProxy::current()->PostTask(
       FROM_HERE,
       base::Bind(&TracingManager::StartTracing,
                  weak_ptr_factory_.GetWeakPtr()));
 }
 
 void TracingManager::OnTraceDataCollected(
     const scoped_refptr<base::RefCountedString>& trace_fragment) {
-  if (current_trace_id_)
+  if (current_trace_id_) {
+    if (!data_.empty())
+      data_ += ",";
     data_ += trace_fragment->data();
+  }
 }
 
 // static
 scoped_ptr<TracingManager> TracingManager::Create() {
   if (g_tracing_manager)
     return scoped_ptr<TracingManager>();
   return scoped_ptr<TracingManager>(new TracingManager());
 }
 
 TracingManager* TracingManager::Get() {
   return g_tracing_manager;
 }