- Previous fix is https://chromium-review.googlesource.com/c/583531 but it
  diverges Scopes created by PreParser from Scopes created by Parser.

- This CL creates the inner block scope a bit earlier and (temporarily) pushes
  it into the scope chain for parsing the variable declarations in a for
  loop. The previous approach was to first parse the variable declarations and
  then reparent the AST nodes / Scopes created while parsing it afterwards.

- This CL partially reverts https://chromium-review.googlesource.com/c/583531;
  the new fix only touches parser-base.h (diff between patch sets 2 and 3 is the
  fix).

- The Ignition golden changes are basically undoing the changes done in that CL
  too.

Bug: chromium:740591
Change-Id: Iceff1383ef066317e754942bb5ff0c70a91bc937
Reviewed-on: https://chromium-review.googlesource.com/603787
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47241}