Add instrumentation hooks to mesaure which subresource filter rules are used.

components/subresource_filter/core/common/url_pattern_index.cc

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/subresource_filter/core/common/url_pattern_index.h"
 
 #include <algorithm>
 #include <limits>
 #include <string>
 
@@ skipping 533 matching lines @@
 }
 
 UrlPatternIndexMatcher::~UrlPatternIndexMatcher() = default;
 
 const flat::UrlRule* UrlPatternIndexMatcher::FindMatch(
     const GURL& url,
     const url::Origin& first_party_origin,
     proto::ElementType element_type,
     proto::ActivationType activation_type,
     bool is_third_party,
-    bool disable_generic_rules) const {
+    bool disable_generic_rules,
+    RuleRecorder* recorder) const {
   if (!flat_index_ || !url.is_valid())
     return nullptr;
   if ((element_type == proto::ELEMENT_TYPE_UNSPECIFIED) ==
       (activation_type == proto::ACTIVATION_TYPE_UNSPECIFIED)) {
     return nullptr;
   }
 
-  return FindMatchInFlatUrlPatternIndex(*flat_index_, url, first_party_origin,
-                                        element_type, activation_type,
-                                        is_third_party, disable_generic_rules);
+  const flat::UrlRule* rule = FindMatchInFlatUrlPatternIndex(
+      *flat_index_, url, first_party_origin, element_type, activation_type,
+      is_third_party, disable_generic_rules);
+
+  // Log the rule if used. We don't care about blacklist or whitelist I assume.
+  // Can we just use url_pattern or are there rules with same pattern
+  // but different options.
+  if (recorder && rule)
+    recorder->RecordRuleUsage(rule);
+  return rule;
 }
 
 }  // namespace subresource_filter