Replaced ToV8Value::toV8Value with V8ValueTraits::toV8Value.

BUG=369451
TEST=no new tests because of just refactoring.

Review URL: https://codereview.chromium.org/350863002

git-svn-id: svn://svn.chromium.org/blink/trunk@177060 bbb929c8-8fbe-4397-9dbb-9b2b20218538