This makes it easier to match VariableProxys against variables in
Scopes (allocation-based prints such as local[0] or context[0] are not
unique).

R=vogelheim@chromium.org

Bug:

Change-Id: I8f86504f5e1657633286561e032805a8f6cff06e
Reviewed-on: https://chromium-review.googlesource.com/467486
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Daniel Vogelheim <vogelheim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44376}