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

components/subresource_filter/core/common/url_pattern_index.cc

Index: components/subresource_filter/core/common/url_pattern_index.cc
diff --git a/components/subresource_filter/core/common/url_pattern_index.cc b/components/subresource_filter/core/common/url_pattern_index.cc
index 574f577a32533c1d0811f55d579d152c22f0a3d7..fdab2ede938d62f70f9ebf593fbf0f259177bb4e 100644
--- a/components/subresource_filter/core/common/url_pattern_index.cc
+++ b/components/subresource_filter/core/common/url_pattern_index.cc
@@ -551,7 +551,8 @@ const flat::UrlRule* UrlPatternIndexMatcher::FindMatch(
     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) ==
@@ -559,9 +560,16 @@ const flat::UrlRule* UrlPatternIndexMatcher::FindMatch(
     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