Add recording of engagement score of external href.

Add recording of AnchorElementMetrics.*.HrefEngagementScoreExternal.

Bug: 850624
Change-Id: I049b5847beb76a80a7c30077373f50079cee061c
Reviewed-on: https://chromium-review.googlesource.com/1157551
Commit-Queue: Lu Chen <chelu@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580003}

chrome/browser/navigation_predictor/navigation_predictor.cc

@@ -137,6 +137,11 @@ void NavigationPredictor::ReportAnchorElementMetricsOnClick(
         "AnchorElementMetrics.Clicked.HrefEngagementScorePositive",
         static_cast<int>(target_score));
   }
+  if (!metrics->is_same_host) {
+    UMA_HISTOGRAM_COUNTS_100(
+        "AnchorElementMetrics.Clicked.HrefEngagementScoreExternal",
+        static_cast<int>(target_score));
+  }
 
   // Look up the clicked URL in |navigation_scores_map_|. Record if we find it.
   auto iter = navigation_scores_map_.find(metrics->target_url.spec());
@@ -285,7 +290,7 @@ void NavigationPredictor::ReportAnchorElementMetricsOnLoad(
         static_cast<int>(metric->is_url_incremented_by_one);
   }
 
-  // Retrive site engagement score of the docuemnt. |metrics| is guaranteed to
+  // Retrieve site engagement score of the document. |metrics| is guaranteed to
   // be non-empty. All |metrics| have the same source_url.
   SiteEngagementService* engagement_service = GetEngagementService();
   double document_engagement_score =
@@ -316,6 +321,11 @@ void NavigationPredictor::ReportAnchorElementMetricsOnLoad(
     UMA_HISTOGRAM_COUNTS_100(
         "AnchorElementMetrics.Visible.HrefEngagementScore2",
         static_cast<int>(target_engagement_score));
+    if (!metric->is_same_host) {
+      UMA_HISTOGRAM_COUNTS_100(
+          "AnchorElementMetrics.Visible.HrefEngagementScoreExternal",
+          static_cast<int>(target_engagement_score));
+    }
 
     // Anchor elements with the same area are assigned with the same rank.
     size_t area_rank = i;

tools/metrics/histograms/histograms.xml

@@ -811,6 +811,17 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram base="true" name="AnchorElementMetrics.HrefEngagementScoreExternal"
+    units="score">
+  <owner>chelu@chromium.org</owner>
+  <owner>tbansal@chromium.org</owner>
+  <summary>
+    The site engagement score of the target link (href) of an anchor element.
+    The score is retrieved from the site engagement service. This histogram is
+    recorded when href is an external link.
+  </summary>
+</histogram>
+
 <histogram base="true" name="AnchorElementMetrics.IsInIFrame" enum="Boolean">
   <owner>chelu@chromium.org</owner>
   <owner>tbansal@chromium.org</owner>
@@ -925,6 +936,7 @@ uploading your change for review.
 <histogram name="AnchorElementMetrics.Visible.NumberOfAnchorElementsAfterMerge"
     units="count">
   <owner>chelu@chromium.org</owner>
+  <owner>tbansal@chromium.org</owner>
   <summary>
     The number of anchor element metrics sent to the browser process on a page
     load. Anchor elements having the same href are merged and counted as 1. This
@@ -116135,6 +116147,7 @@ uploading your change for review.
   <affected-histogram name="AnchorElementMetrics.ContainsImage"/>
   <affected-histogram name="AnchorElementMetrics.DocumentEngagementScore"/>
   <affected-histogram name="AnchorElementMetrics.HrefEngagementScore2"/>
+  <affected-histogram name="AnchorElementMetrics.HrefEngagementScoreExternal"/>
   <affected-histogram name="AnchorElementMetrics.IsInIFrame"/>
   <affected-histogram name="AnchorElementMetrics.IsSameHost"/>
   <affected-histogram name="AnchorElementMetrics.IsUrlIncrementedByOne"/>