Revert "Remove GrProgramDesc::KeyHeader structure"

This reverts commit 4bcd58afbf1a1993e453231c575b47a0ae1ec24d.

Reason for revert: Possible issue with copying/assignment

Original change's description:
> Remove GrProgramDesc::KeyHeader structure
>
> Instead, just fold all of this information into the key, like everything
> else. The only value that was accessed elsewhere is the initial key
> length. That doesn't need to be part of the key, so store it separately
> in the GrProgramDesc.
>
> Removing this special case logic is just the first step in revising how
> we assemble keys.
>
> Bug: skia:11372
> Change-Id: I52eb76812045e1906797cb37e809cfd0b3332ef0
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/376797
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>

TBR=bsalomon@google.com,robertphillips@google.com,brianosman@google.com

Change-Id: I58b39a173abc45cd4932fd758fa005d1f727a0d9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:11372
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/376848
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed