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

tools/android/forwarder2/host_forwarder_main.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 <errno.h>
 #include <signal.h>
 #include <unistd.h>
 
 #include <cstdio>
 #include <cstring>
 #include <string>
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/file_util.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/memory/scoped_vector.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/safe_strerror_posix.h"
 #include "base/string_number_conversions.h"
-#include "base/string_piece.h"
 #include "base/string_util.h"
 #include "base/stringprintf.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/string_split.h"
 #include "tools/android/forwarder2/common.h"
 #include "tools/android/forwarder2/daemon.h"
 #include "tools/android/forwarder2/host_controller.h"
 #include "tools/android/forwarder2/pipe_notifier.h"
 #include "tools/android/forwarder2/socket.h"
 
 namespace forwarder2 {
 namespace {
 
@@ skipping 219 matching lines @@
 
   return client_delegate.has_failed() || daemon_delegate.has_failed();
 }
 
 }  // namespace
 }  // namespace forwarder2
 
 int main(int argc, char** argv) {
   return forwarder2::RunHostForwarder(argc, argv);
 }