Previously we'd have a scope in the main zone, and another in the temp zone. Then we carefully copied back data to the main zone. This CL changes it so that the scope is just fixed up to only contain data from the main zone. That avoids additional copies and additional allocations; while not increasing the care that needs to be taken. This will also make it easier to abort preparsing while parsing using a temp zone.

BUG=

Committed: https://crrev.com/f41e7ebd62b32e861b6aa14ad8bfce3018d03c3c
Review-Url: https://codereview.chromium.org/2368313002
Cr-Original-Commit-Position: refs/heads/master@{#39800}
Cr-Commit-Position: refs/heads/master@{#39828}