predictors: Collect page load metrics for ResourcePrefetchPredictor.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 778bde8307e04d91858887fe90fe838ec55fbd2d..a317d08d6e44d6fe4da031d0048caf2ae2ad7937 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -115682,6 +115682,28 @@ value.
       name="PageLoad.PaintTiming.NavigationToFirstContentfulPaint"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="PageLoadMetricsClientsResourcePrefetchPredictor"
+    separator="." ordering="prefix">
+  <suffix base="true" name="Clients.ResourcePrefetchPredictor"
+      label="PageLoadMetrics with enabled ResourcePrefetchPredictor"/>
+  <affected-histogram
+      name="PageLoad.Experimental.PaintTiming.NavigationToFirstMeaningfulPaint"/>
+  <affected-histogram
+      name="PageLoad.PaintTiming.NavigationToFirstContentfulPaint"/>
+</histogram_suffixes>
+
+<histogram_suffixes
+    name="PageLoadMetricsClientsResourcePrefetchPredictorPrefetchingType"
+    separator=".">
+  <suffix name="Prefetchable"
+      label="The predictor database contained subresources for prediction for
+             a page"/>
+  <affected-histogram
+      name="PageLoad.Clients.ResourcePrefetchPredictor.Experimental.PaintTiming.NavigationToFirstMeaningfulPaint"/>
+  <affected-histogram
+      name="PageLoad.Clients.ResourcePrefetchPredictor.PaintTiming.NavigationToFirstContentfulPaint"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="PageLoadMetricsClientsServiceWorker" separator="."
     ordering="prefix">
   <suffix name="Clients.ServiceWorker"