Write loading signal extra data in JSON

chrome/browser/android/offline_pages/prerendering_offliner.cc

 // Copyright 2016 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/android/offline_pages/prerendering_offliner.h"
 
 #include "base/bind.h"
+#include "base/json/json_writer.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/sys_info.h"
 #include "chrome/browser/android/offline_pages/offline_page_mhtml_archiver.h"
 #include "chrome/browser/android/offline_pages/offliner_helper.h"
 #include "chrome/browser/profiles/profile.h"
 #include "components/offline_pages/core/background/offliner_policy.h"
 #include "components/offline_pages/core/background/save_page_request.h"
 #include "components/offline_pages/core/client_namespace_constants.h"
 #include "components/offline_pages/core/downloads/download_ui_adapter.h"
 #include "components/offline_pages/core/offline_page_feature.h"
@@ skipping 99 matching lines @@
     // Clear pending request and app listener then run completion callback.
     pending_request_.reset(nullptr);
     app_listener_.reset(nullptr);
     completion_callback_.Run(request, load_status);
   }
 }
 
 std::string PrerenderingOffliner::SerializeLoadingSignalData() {
   // Write the signal data into a single string.
   std::string signal_string;
-  const std::vector<std::string>& signals = loader_->GetLoadingSignalData();
+  const base::DictionaryValue& signals = loader_->GetLoadingSignalData();
 
-  // TODO(petewil): Convert this to JSON, use json_writer.h
-  for (std::string signal : signals) {
-    signal_string += signal;
-    signal_string += "\n";
-  }
+  base::JSONWriter::Write(signals, &signal_string);
+
   return signal_string;
 }
 
 void PrerenderingOffliner::OnSavePageDone(
     const SavePageRequest& request,
     SavePageResult save_result,
     int64_t offline_id) {
   // Check if request is still pending receiving a callback.
   if (!pending_request_)
     return;
@@ skipping 179 matching lines @@
 void PrerenderingOffliner::HandleApplicationStateChangeCancel(
     const SavePageRequest& request,
     int64_t offline_id) {
   // This shouldn't be immediate, but account for case where request was reset
   // while waiting for callback.
   if (pending_request_ && pending_request_->request_id() != offline_id)
     return;
   completion_callback_.Run(request, RequestStatus::FOREGROUND_CANCELED);
 }
 }  // namespace offline_pages