Update GrResourceCache changeUniqueKey to stay in valid state after each step

The issues are that we are intertwining removing things from the old and new
resource. This changes it so we do all the removal on the old resource first
then start updating the new resource.

Bug: skia:
Change-Id: I7ce4a309290cd499cdc4398c87d1cfd42ef6994d
Reviewed-on: https://skia-review.googlesource.com/44242
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
1 file changed