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

string_piece.h was moved into base/strings/ in r191206 -
https://chromiumcodereview.appspot.com/12982018/

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Review URL: https://codereview.chromium.org/14272007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@194693 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/dbus/object_proxy.h b/dbus/object_proxy.h
index 61576e6..23c0f4c 100644
--- a/dbus/object_proxy.h
+++ b/dbus/object_proxy.h
@@ -13,7 +13,7 @@
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 #include "base/time.h"
 #include "dbus/dbus_export.h"
 #include "dbus/object_path.h"