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

content/browser/host_zoom_map_impl.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 "content/browser/host_zoom_map_impl.h"
+
 #include <cmath>
 
-#include "content/browser/host_zoom_map_impl.h"
-
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "content/browser/renderer_host/render_process_host_impl.h"
 #include "content/browser/renderer_host/render_view_host_impl.h"
 #include "content/common/view_messages.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/resource_context.h"
@@ skipping 224 matching lines @@
     }
     default:
       NOTREACHED() << "Unexpected preference observed.";
   }
 }
 
 HostZoomMapImpl::~HostZoomMapImpl() {
 }
 
 }  // namespace content