Remove deprecated API usaged in SerializedScriptValue.cpp

R=mkwst@chromium.org
BUG=324225

Review URL: https://codereview.chromium.org/94933002

git-svn-id: svn://svn.chromium.org/blink/trunk@162838 bbb929c8-8fbe-4397-9dbb-9b2b20218538