Write loading signal extra data in JSON

chrome/browser/android/offline_pages/prerendering_loader.h

 // 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.
 
 #ifndef CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_LOADER_H_
 #define CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_LOADER_H_
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
+#include "base/values.h"
 #include "chrome/browser/android/offline_pages/prerender_adapter.h"
 #include "components/offline_pages/core/background/offliner.h"
 #include "components/offline_pages/core/snapshot_controller.h"
 
 class GURL;
 
 namespace content {
 class BrowserContext;
 class WebContents;
 }  // namespace content
@@ skipping 54 matching lines @@
   void OnPrerenderDomContentLoaded() override;
   void OnPrerenderStop() override;
   void OnPrerenderNetworkBytesChanged(int64_t bytes) override;
 
   // SnapshotController::Client implementation:
   void StartSnapshot() override;
 
   // Returns true if the lowbar of snapshotting a page is met.
   virtual bool IsLowbarMet();
 
-  // Returns a vector of strings for analysis of loading progress.
-  const std::vector<std::string>& GetLoadingSignalData() {
-    return signal_data_;
-  }
+  // Returns a JSON dictionary value for analysis of loading progress.
+  const base::DictionaryValue& GetLoadingSignalData() { return signal_data_; }
 
  private:
   // State of the loader (only one request may be active at a time).
   enum class State {
     IDLE,     // No active load request.
     PENDING,  // Load request is pending the start of prerendering.
     LOADING,  // Loading in progress.
     LOADED,   // Loaded and now waiting for requestor to StopLoading().
   };
 
@@ skipping 26 matching lines @@
   content::BrowserContext* browser_context_;
 
   // Adapter for handling calls to the prerender stack.
   std::unique_ptr<PrerenderAdapter> adapter_;
 
   // A WebContents for the active load request that is used to hold the session
   // storage namespace for rendering. This will NOT have the loaded page.
   std::unique_ptr<content::WebContents> session_contents_;
 
   // Signal data collected for this rendering attempt
-  std::vector<std::string> signal_data_;
+  base::DictionaryValue signal_data_;
 
   // Callback to call when the active load request completes, fails, or is
   // canceled.
   LoadPageCallback load_done_callback_;
 
   // Callback to call when we know more bytes have loaded from the network.
   ProgressCallback progress_callback_;
 
   // True if the lowbar of snapshotting a page is met.
   bool is_lowbar_met_;
 
   // Time in ticks of when we start loading the page.
   base::TimeTicks load_start_time_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderingLoader);
 };
 
 }  // namespace offline_pages
 
 #endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_LOADER_H_