Make ExtensionIconSet::ContainsPath use StringPiece.

extensions/common/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.
 
 import("//build/config/features.gni")
 import("//extensions/features/features.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 
 source_set("common_constants") {
   sources = [
@@ skipping 290 matching lines @@
   }
 
   source_set("unit_tests") {
     testonly = true
     sources = [
       "api/declarative/declarative_manifest_unittest.cc",
       "api/printer_provider/usb_printer_manifest_unittest.cc",
       "api/sockets/sockets_manifest_permission_unittest.cc",
       "csp_validator_unittest.cc",
       "event_filter_unittest.cc",
+      "extension_icon_set_unittest.cc",
       "extension_l10n_util_unittest.cc",
       "extension_messages_unittest.cc",
       "extension_resource_unittest.cc",
       "extension_set_unittest.cc",
       "features/base_feature_provider_unittest.cc",
       "features/complex_feature_unittest.cc",
       "features/simple_feature_unittest.cc",
       "file_util_unittest.cc",
       "image_util_unittest.cc",
       "manifest_handler_unittest.cc",
@@ skipping 38 matching lines @@
       "//extensions/strings",
       "//ipc",
       "//testing/gmock",
       "//testing/gtest",
       "//ui/base",
       "//ui/gfx",
       "//url",
     ]
   }
 }  # enable_extensions