Also adds a unit test to make sure readIntVector and writeIntVector
match.  It was not immediately clear that writing the vector size in
writeIntVector is writing an int instead of a size_t.

Bug: angleproject:3394
Change-Id: I09a003c169dbc47e40c0cd3e4da6f1d7a905c6da
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1983162Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>