Add support for counting same-document AMP loads.

chrome/browser/page_load_metrics/observers/amp_page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/observers/amp_page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/observers/amp_page_load_metrics_observer.h b/chrome/browser/page_load_metrics/observers/amp_page_load_metrics_observer.h
index 5225b74c36330392bceb7d30ba5b39b4dec659af..53529a2f7fce638c3c5ec69639c7383ffca574fb 100644
--- a/chrome/browser/page_load_metrics/observers/amp_page_load_metrics_observer.h
+++ b/chrome/browser/page_load_metrics/observers/amp_page_load_metrics_observer.h
@@ -31,6 +31,9 @@ class AMPPageLoadMetricsObserver
     AMP_CACHE,
     GOOGLE_SEARCH_AMP_VIEWER,
     GOOGLE_NEWS_AMP_VIEWER,
+
+    // New values should be added before this final entry.
+    AMP_VIEW_TYPE_LAST
   };
 
   static AMPViewType GetAMPViewType(const GURL& url);
@@ -40,6 +43,8 @@ class AMPPageLoadMetricsObserver
 
   // page_load_metrics::PageLoadMetricsObserver:
   ObservePolicy OnCommit(content::NavigationHandle* navigation_handle) override;
+  void OnCommitSameDocumentNavigation(
+      content::NavigationHandle* navigation_handle) override;
   void OnDomContentLoadedEventStart(
       const page_load_metrics::PageLoadTiming& timing,
       const page_load_metrics::PageLoadExtraInfo& info) override;
@@ -55,6 +60,8 @@ class AMPPageLoadMetricsObserver
                     const page_load_metrics::PageLoadExtraInfo& info) override;
 
  private:
+  GURL committed_url_;
+  GURL last_same_document_url_;
   AMPViewType view_type_ = AMPViewType::NONE;
 
   DISALLOW_COPY_AND_ASSIGN(AMPPageLoadMetricsObserver);