Aggregate DocumentSubresourceFilter counters on page level.

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 224814a18431e6aa6824392aac58e2e62d33157c..b843f5be0db8f4a1416c5f37dbc36519c151c94e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -64860,6 +64860,49 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SubresourceFilter.PageLoad.NumSubresourceLoads.Disallowed"
+    units="resource loads">
+  <owner>pkalinnikov@chromium.org</owner>
+  <summary>
+    Whenever a page load is finished with subresource filtering activated,
+    records the total number of subresource loads that have been disallowed.
+    This only differs from `MatchedRules` when filtering is performed in dry-run
+    mode.
+  </summary>
+</histogram>
+
+<histogram name="SubresourceFilter.PageLoad.NumSubresourceLoads.Evaluated"
+    units="resource loads">
+  <owner>pkalinnikov@chromium.org</owner>
+  <summary>
+    Whenever a page load is finished with subresource filtering activated,
+    records the total number of subresource loads that have been evaluated. This
+    only differs from 'Total' when some of subdocuments is subject to a
+    deactivating rule with DOCUMENT activation type.
+  </summary>
+</histogram>
+
+<histogram name="SubresourceFilter.PageLoad.NumSubresourceLoads.MatchedRules"
+    units="resource loads">
+  <owner>pkalinnikov@chromium.org</owner>
+  <summary>
+    Whenever a page load is finished with subresource filtering activated,
+    records the total number of subresource loads that have matched filtering
+    rules. This only differs from `Disallowed` when filtering is performed in
+    dry-run mode.
+  </summary>
+</histogram>
+
+<histogram name="SubresourceFilter.PageLoad.NumSubresourceLoads.Total"
+    units="resource loads">
+  <owner>pkalinnikov@chromium.org</owner>
+  <summary>
+    Whenever a page load is finished with subresource filtering activated,
+    records the total number of subresource loads that have gone through the
+    subresource filtering pipeline.
+  </summary>
+</histogram>
+
 <histogram name="SubresourceFilter.PageLoad.RedirectChainLength" units="urls">
   <owner>melandory@chromium.org</owner>
   <summary>Total length of the server redirects during the navigation.</summary>