Introduce ContentSettingsClient interface

components/content_settings/core/browser/BUILD.gn

 # Copyright 2014 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.
 
 static_library("browser") {
   sources = [
+    "content_settings_client.cc",
+    "content_settings_client.h",
     "content_settings_details.cc",
     "content_settings_details.h",
     "content_settings_observer.h",
     "content_settings_provider.h",
     "content_settings_observable_provider.cc",
     "content_settings_observable_provider.h",
     "content_settings_origin_identifier_value_map.cc",
     "content_settings_origin_identifier_value_map.h",
     "content_settings_rule.cc",
     "content_settings_rule.h",
     "local_shared_objects_counter.h",
   ]
 
   deps = [
     "//base",
     "//components/content_settings/core/common",
   ]
 }
 
+static_library("browser_test_utils") {
+  sources = [
+    "stub_content_settings_client.cc",
+    "stub_content_settings_client.h",
+    "stub_local_shared_objects_counter.cc",
+    "stub_local_shared_objects_counter.h",
+  ]
+
+  deps = [
+    "//base",
+  ]
+}
+
 source_set("unit_tests") {
   testonly = true
   sources = [
     "content_settings_rule_unittest.cc",
   ]
 
   deps = [
     ":browser",
     "//testing/gtest",
   ]
 }