Move some methods of VertexDataManager to helper methods. Refactoring patch only. BUG=angle:571 Change-Id: Ic318b4c4366e33b8d33f6003dd39f660f40d354a Reviewed-on: https://chromium-review.googlesource.com/210649 Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org>