This patch extends ExtractContextReferences to handle all declaration
contexts, not only function/module/eval contexts.

Bug: chromium:817954
Change-Id: Ibe2827a9d6b2939552da26a60df959c9b22ea059
Reviewed-on: https://chromium-review.googlesource.com/962763
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51945}