Update the V8 version for Chromium branch 86.

This is a roll-back to 8.6.395. 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.

R=machenbach@chromium.org,vahl@chromium.org

Change-Id: Ib03e3f3232c358f2e2d3410cfd596fe9533ccf90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2366796Reviewed-by: Michael Hablich <hablich@chromium.org>
Commit-Queue: Lutz Vahl <vahl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800100}

DEPS

@@ -199,7 +199,7 @@ 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': '899af242de4cac909e414d3d94d2c7cab1707cad',
+  'v8_revision': 'a64aed2333abf49e494d2a5ce24bbd14fff19f60',
   # 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.