[safe-browsing] Log prefix check in microseconds

Most prefix checks take between 0 and 1 ms. This CL improves the
resolution by logging the check in micros.

The CL also removes the SB2.FilterCheck metric which is not really
needed anymore.

Bug: 787092
Change-Id: I18a81d6eb7891f5a4c8c6fd6e7e956dc653d5379
Reviewed-on: https://chromium-review.googlesource.com/960248
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542976}

chrome/browser/safe_browsing/local_database_manager.cc

@@ -514,8 +514,6 @@ bool LocalSafeBrowsingDatabaseManager::CheckBrowseUrl(
   prefix_hits.erase(std::unique(prefix_hits.begin(), prefix_hits.end()),
                     prefix_hits.end());
 
-  UMA_HISTOGRAM_TIMES("SB2.FilterCheck", base::TimeTicks::Now() - start);
-
   if (prefix_hits.empty() && cache_hits.empty())
     return true;  // URL is okay.
 

components/safe_browsing/db/v4_local_database_manager.cc

@@ -18,6 +18,7 @@
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/string_util.h"
 #include "base/task_scheduler/post_task.h"
+#include "base/timer/elapsed_timer.h"
 #include "components/safe_browsing/db/notification_types.h"
 #include "components/safe_browsing/db/v4_feature_list.h"
 #include "components/safe_browsing/db/v4_protocol_manager_util.h"
@@ -26,7 +27,6 @@
 #include "crypto/sha2.h"
 
 using content::BrowserThread;
-using base::TimeTicks;
 
 namespace safe_browsing {
 
@@ -634,8 +634,7 @@ bool V4LocalDatabaseManager::GetPrefixMatches(
   DCHECK(enabled_);
   DCHECK(v4_database_);
 
-  const base::TimeTicks before = TimeTicks::Now();
-
+  base::ElapsedTimer timer;
   full_hash_to_store_and_hash_prefixes->clear();
   for (const auto& full_hash : check->full_hashes) {
     StoreAndHashPrefixes matched_store_and_hash_prefixes;
@@ -647,16 +646,11 @@ bool V4LocalDatabaseManager::GetPrefixMatches(
     }
   }
 
-  // TODO(vakh): Only log SafeBrowsing.V4GetPrefixMatches.Time once PVer3 code
-  // is removed.
   // NOTE(vakh): This doesn't distinguish which stores it's searching through.
   // However, the vast majority of the entries in this histogram will be from
   // searching the three CHECK_BROWSE_URL stores.
-  base::TimeDelta diff = TimeTicks::Now() - before;
-  UMA_HISTOGRAM_TIMES("SB2.FilterCheck", diff);
-  UMA_HISTOGRAM_CUSTOM_TIMES("SafeBrowsing.V4GetPrefixMatches.Time", diff,
-                             base::TimeDelta::FromMicroseconds(20),
-                             base::TimeDelta::FromSeconds(1), 50);
+  UMA_HISTOGRAM_COUNTS_10M("SafeBrowsing.V4GetPrefixMatches.TimeUs",
+                           timer.Elapsed().InMicroseconds());
   return !full_hash_to_store_and_hash_prefixes->empty();
 }
 

tools/metrics/histograms/histograms.xml

@@ -75383,6 +75383,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="SafeBrowsing.V4GetPrefixMatches.Time" units="ms">
+  <obsolete>
+    Deprecated in favor of the TimeUs variant
+  </obsolete>
   <owner>vakh@chromium.org</owner>
   <summary>
     The time that it took to check a URL against our in-memory database. It is
@@ -75390,6 +75393,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SafeBrowsing.V4GetPrefixMatches.TimeUs" units="microseconds">
+  <owner>csharrison@chromium.org</owner>
+  <owner>vakh@chromium.org</owner>
+  <summary>
+    The time that it took to check a URL against our in-memory database. It is
+    dominated by the time to perform checks for CheckBrowseUrl. Note that this
+    metric is recorded even for users with low resolution clocks.
+  </summary>
+</histogram>
+
 <histogram name="SafeBrowsing.V4MergeUpdateTime" units="ms">
   <obsolete>
     Replaced by SafeBrowsing.V4*.MergeUpdate.Time.
@@ -76208,6 +76221,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="SB2.FilterCheck" units="ms">
+  <obsolete>
+    Deprecated in favor of SafeBrowsing.V4GetPrefixMatches.TimeUs
+  </obsolete>
   <owner>vakh@chromium.org</owner>
   <summary>
     The time that it took to check a URL against our in-memory filter.