ANGLE's internal hash maps would run MurmurHash on c++ structs to
come up with hash values. Since the hash ran on 4 byte words only,
it would have no understanding that sometimes our structs would only
have meaninful data in the first N bytes, and would include the
garbage at the end in the hash calculation. This fixes the problem by
forcing our structs to be aligned at compile-time.

It also adds custom copy operators for a few classes to ensure that
all bits are copied when the struct is initialized, including the
padding.

Bug: angleproject:1569
Bug: chromium:721648
Change-Id: I4d11f6e12d9a067b36e1416c7ed15586eff99aab
Reviewed-on: https://chromium-review.googlesource.com/783990
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>