Update the remaining include paths of base/string_piece.h to its new location.

cc/trees/layer_tree_host_perftest.cc

 // Copyright 2012 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.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include "base/file_util.h"
 #include "base/files/file_path.h"
 #include "base/path_service.h"
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 #include "cc/layers/content_layer.h"
 #include "cc/layers/nine_patch_layer.h"
 #include "cc/layers/solid_color_layer.h"
 #include "cc/test/fake_content_layer_client.h"
 #include "cc/test/layer_tree_json_parser.h"
 #include "cc/test/layer_tree_test.h"
 #include "cc/test/paths.h"
 
 namespace cc {
 namespace {
@@ skipping 115 matching lines @@
   scoped_refptr<Layer> scrollable_;
 };
 
 TEST_F(ScrollingLayerTreePerfTest, LongScrollablePage) {
   ReadTestFile("long_scrollable_page");
   RunTest(false);
 }
 
 }  // namespace
 }  // namespace cc