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 ff785ad4851976ab1311890758905ae9b6a072d2..d767e89931874e1ea2db04a93ffca859aa7decc6 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -64340,6 +64340,49 @@ 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 document load is finished in a main frame or subframe with

[engedy, 2016/12/28 09:36:02]

nit: Update this line.

[pkalinnikov, 2016/12/28 13:43:23]

Done.

+    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>