V8CollectableDuringMinorGCFlag should not be taken over to the next GC

A minor GC prologue sets V8CollectableDuringMinorGCFlags, but all of the flags need to be cleared before the minor GC prologue finishes. These flags should not be taken over to the next GC.

For more details, see the comment in the CL.

TEST=none (This is a potential bug fix and I couldn't reproduce the bug.)

Review URL: https://codereview.chromium.org/108453005

git-svn-id: svn://svn.chromium.org/blink/trunk@164659 bbb929c8-8fbe-4397-9dbb-9b2b20218538