Adding MHTML support into Page Load Metrics

chrome/browser/page_load_metrics/observers/previews_page_load_metrics_observer.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_PAGE_LOAD_METRICS_OBSERVERS_PREVIEWS_PAGE_LOAD_METRICS_OBSERVER_H_
 #define CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_PREVIEWS_PAGE_LOAD_METRICS_OBSERVER_H_
 
+#include <string>
+
 #include "base/macros.h"
 #include "chrome/browser/page_load_metrics/page_load_metrics_observer.h"
 
 namespace content {
 class NavigationHandle;
 class WebContents;
 }
 
 namespace page_load_metrics {
 struct PageLoadExtraInfo;
@@ skipping 29 matching lines @@
   void OnLoadEventStart(
       const page_load_metrics::PageLoadTiming& timing,
       const page_load_metrics::PageLoadExtraInfo& info) override;
   void OnFirstLayout(const page_load_metrics::PageLoadTiming& timing,
                      const page_load_metrics::PageLoadExtraInfo& info) override;
   void OnFirstContentfulPaint(
       const page_load_metrics::PageLoadTiming& timing,
       const page_load_metrics::PageLoadExtraInfo& info) override;
   void OnParseStart(const page_load_metrics::PageLoadTiming& timing,
                     const page_load_metrics::PageLoadExtraInfo& info) override;
+  ObservePolicy ShouldObserveMimeType(
+      const std::string& mime_type) const override;
 
  private:
   // Whether |web_contents| is showing an offline pages preview. Overridden in
   // testing.
   virtual bool IsOfflinePreview(content::WebContents* web_contents) const;
 
   DISALLOW_COPY_AND_ASSIGN(PreviewsPageLoadMetricsObserver);
 };
 
 }  // namespace previews
 
 #endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_PREVIEWS_PAGE_LOAD_METRICS_OBSERVER_H_