Backend for css rule tracking

third_party/WebKit/Source/core/css/BUILD.gn

 # Copyright 2016 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.
 
 import("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("css") {
   split_count = 5
   sources = [
     "ActiveStyleSheets.cpp",
@@ skipping 358 matching lines @@
     "resolver/StyleAdjuster.h",
     "resolver/StyleBuilderConverter.cpp",
     "resolver/StyleBuilderConverter.h",
     "resolver/StyleBuilderCustom.cpp",
     "resolver/StyleResolver.cpp",
     "resolver/StyleResolver.h",
     "resolver/StyleResolverState.cpp",
     "resolver/StyleResolverState.h",
     "resolver/StyleResolverStats.cpp",
     "resolver/StyleResolverStats.h",
+    "resolver/StyleRuleUsageTracker.cpp",
+    "resolver/StyleRuleUsageTracker.h",
     "resolver/StyleSharingDepthScope.h",
     "resolver/TransformBuilder.cpp",
     "resolver/TransformBuilder.h",
     "resolver/ViewportStyleResolver.cpp",
     "resolver/ViewportStyleResolver.h",
   ]
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }