There was only one case where this wasn't the case, having to do with
variable declarations, and for that case the information need not
actually be stored on the block, but should rather be propagated
to the VariableProxy.

Bug: v8:6092
Change-Id: I0d0025ec73d3dd4f9402606105d3e883a9417283
Reviewed-on: https://chromium-review.googlesource.com/639911
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47692}