Oilpan: Initialize the size of InterporableValue::m_values in the constructor

This is a simple follow-up CL for r170298.
We should initialize the vector in the constructor and avoid calling resize().

Review URL: https://codereview.chromium.org/216173006

git-svn-id: svn://svn.chromium.org/blink/trunk@170328 bbb929c8-8fbe-4397-9dbb-9b2b20218538