*re-land with fix for cache overflowing*

Using a much more compact input layout structure allows us to save
quite a bit of time comparing input layouts, or computing hashes.
A subsequent patch shrinks the size of the structure further.

BUG=angleproject:959

Change-Id: If240bb7c84d78fc8c9fb6f9049bf71d8a81c97c6
Reviewed-on: https://chromium-review.googlesource.com/283227Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>