If an attribute was never enabled or disabled the default state was not
properly synced in our implementation. This wasn't caught by currently
enabled tests. Those tests are now enabled in VertexAttributeTest.

Bug: angleproject:2800
Change-Id: I97c063651911379e16de4ee557d9840782114c54
Reviewed-on: https://chromium-review.googlesource.com/1199724Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>