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

ui/base/resource/data_pack_unittest.cc

 // Copyright (c) 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 "base/file_util.h"
 #include "base/files/file_path.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/path_service.h"
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/base/resource/data_pack.h"
 
 namespace ui {
 
 class DataPackTest
     : public testing::TestWithParam<DataPack::TextEncodingType> {
  public:
   DataPackTest() {}
 };
@@ skipping 121 matching lines @@
   EXPECT_EQ(two, data);
   ASSERT_TRUE(pack.GetStringPiece(3, &data));
   EXPECT_EQ(three, data);
   ASSERT_TRUE(pack.GetStringPiece(4, &data));
   EXPECT_EQ(four, data);
   ASSERT_TRUE(pack.GetStringPiece(15, &data));
   EXPECT_EQ(fifteen, data);
 }
 
 }  // namespace ui