[url_pattern_index] Print matching rule for tracing

This is useful for debugging.

Bug: None
Change-Id: I8e6260f09b3c17f0a9952739387f70a431571011
Reviewed-on: https://chromium-review.googlesource.com/c/1308013
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603990}

components/subresource_filter/tools/BUILD.gn

@@ -15,7 +15,7 @@ static_library("tools_lib") {
     "../core/browser",
     "../core/common",
     "//base",
-    "//components/url_pattern_index:util",
+    "//components/url_pattern_index",
     "//url",
   ]
 }

components/url_pattern_index/BUILD.gn

@@ -14,6 +14,8 @@ static_library("url_pattern_index") {
     "url_pattern.h",
     "url_pattern_index.cc",
     "url_pattern_index.h",
+    "url_rule_util.cc",
+    "url_rule_util.h",
   ]
 
   public_deps = [
@@ -44,17 +46,6 @@ static_library("test_support") {
   ]
 }
 
-static_library("util") {
-  sources = [
-    "url_rule_util.cc",
-    "url_rule_util.h",
-  ]
-  deps = [
-    ":url_pattern_index",
-    "//base",
-  ]
-}
-
 source_set("unit_tests") {
   testonly = true
   sources = [
@@ -69,7 +60,6 @@ source_set("unit_tests") {
   deps = [
     ":test_support",
     ":url_pattern_index",
-    ":util",
     "//base",
     "//testing/gtest",
     "//third_party/protobuf:protobuf_lite",

components/url_pattern_index/url_pattern_index.cc

@@ -17,8 +17,10 @@
 #include "base/optional.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
+#include "base/trace_event/trace_event.h"
 #include "components/url_pattern_index/ngram_extractor.h"
 #include "components/url_pattern_index/url_pattern.h"
+#include "components/url_pattern_index/url_rule_util.h"
 #include "url/gurl.h"
 #include "url/origin.h"
 #include "url/url_constants.h"
@@ -793,9 +795,15 @@ const flat::UrlRule* UrlPatternIndexMatcher::FindMatch(
     return nullptr;
   }
 
-  return FindMatchInFlatUrlPatternIndex(
+  auto* rule = FindMatchInFlatUrlPatternIndex(
       *flat_index_, UrlPattern::UrlInfo(url), first_party_origin, element_type,
       activation_type, is_third_party, disable_generic_rules, strategy);
+  if (rule) {
+    TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("loading"),
+                 "UrlPatternIndexMatcher::FindMatch", "pattern",
+                 FlatUrlRuleToFilterlistString(rule));
+  }
+  return rule;
 }
 
 }  // namespace url_pattern_index