Update the V8 version for Chromium branch 69.

This is a roll-back to V8 6.9.427. This is the most stable candidate out of the latest Canaries.

If this commit results in failures in Blink please contact the Blink sheriff. They may need to make changes to Blink because of the roll-back.

When in doubt please try to contact the committer and reviewers of this CL before reverting it.

TBR=machenbach@chromium.org
NOTRY=true

Change-Id: I4d7f1c1a1408f37cfcab66001ceba90851183cb3
Reviewed-on: https://chromium-review.googlesource.com/1143278
Commit-Queue: Michael Hablich <hablich@chromium.org>
Reviewed-by: Michael Hablich <hablich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576464}

DEPS

@@ -109,7 +109,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.
-  'v8_revision': '6014ce844cec377c154605a0b848c8b2faf8b853',
+  'v8_revision': 'd7b61abe7b48928aed739f02bf7695732d359e7e',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling swarming_client
   # and whatever else without interference from each other.