[subresource_filter] SB throttle can send multiple speculative requests.

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 ce92b4a4b9b3383ccff650ee1c5c910ff9b38b75..3fd9bf431c0025cd151a498e94e299657278924b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -70932,6 +70932,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SubresourceFilter.PageLoad.SafeBrowsingDelay" units="ms">
+  <owner>csharrison@chromium.org</owner>
+  <summary>
+    The navigation delay imposed by the subresource filter on a given navigation
+    due to Safe Browsing checks.
+  </summary>
+</histogram>
+
 <histogram
     name="SubresourceFilter.PageLoad.SubresourceEvaluation.TotalCPUDuration"
     units="microseconds">
@@ -70974,6 +70982,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SubresourceFilter.SafeBrowsing.CheckTime" units="ms">
+  <owner>csharrison@chromium.org</owner>
+  <summary>
+    The time an individual Safe Browsing URL check took before finishing. Logged
+    when a check is complete or cancelled due to a timeout.
+  </summary>
+</histogram>
+
 <histogram name="SubresourceFilter.SubresourceLoad.Evaluation.CPUDuration"
     units="microseconds">
   <owner>pkalinnikov@chromium.org</owner>