base: Update the 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/

TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/13374002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@191508 0039d316-1c4b-4281-b951-d872f2087c98


CrOS-Libchrome-Original-Commit: eb62f726194d68406047f2716e8ef500bf456d67
diff --git a/base/json/json_reader_unittest.cc b/base/json/json_reader_unittest.cc
index 353e095..4cf1d37 100644
--- a/base/json/json_reader_unittest.cc
+++ b/base/json/json_reader_unittest.cc
@@ -9,7 +9,7 @@
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/path_service.h"
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "build/build_config.h"