Add page-level aggregation of SubresourceFilter time metrics.

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 11ae958f7a0f39ca8f319a4afb6316f184005c50..1dbfa06b08bc3dd644704a6167e1487a60190c74 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -64358,6 +64358,29 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram
+    name="SubresourceFilter.PageLoad.SubresourceEvaluation.TotalCPUDuration"
+    units="microseconds">
+  <owner>pkalinnikov@chromium.org</owner>
+  <summary>
+    Whenever a page load is finished with subresource filtering activated,
+    records the total thread CPU time spent by dependent
+    DocumentSubresourceFilters on processing subresource requests in allowLoad.

[engedy, 2016/12/19 10:18:42]

Phrasing nit (same below):

... spent on evaluating subresource requests, aggregated across all frames.

[pkalinnikov, 2016/12/21 15:28:46]

Done.

+  </summary>
+</histogram>
+
+<histogram
+    name="SubresourceFilter.PageLoad.SubresourceEvaluation.TotalWallDuration"
+    units="microseconds">
+  <owner>pkalinnikov@chromium.org</owner>
+  <summary>
+    Whenever a page load is finished with subresource filtering activated,
+    records the total real time spent by dependent DocumentSubresourceFilters on
+    processing subresource requests in allowLoad, including the time spent on
+    waiting or being descheduled.
+  </summary>
+</histogram>
+
 <histogram name="SubresourceFilter.Prompt.NumReloads" enum="BooleanRequested">
   <owner>melandory@chromium.org</owner>
   <summary>