When traverseing an accessor expression, stop as soon as we hit a
source object that has a constant value. This prevents us from trying
to emit expressions that have abstract types and no materialization
nodes.
Bug: chromium:1442551
Change-Id: I8296ae58e63624e647052cdf966dbff15630a4d8
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/132040
Auto-Submit: James Price <jrprice@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>