Revert "Update V8 to version 6.8.184.1 (cherry-pick)."

This reverts commit c0e58526.

Reason for revert: speculative attempt to fix http://crbug.com/840988

Original change's description:
> Update V8 to version 6.8.184.1 (cherry-pick).
> 
> Summary of changes available at:
> https://chromium.googlesource.com/v8/v8/+log/e3f3bcb2..9ef8a461
> 
> Please follow these instructions for assigning/CC'ing issues:
> https://github.com/v8/v8/wiki/Triaging%20issues
> 
> Please close rolling in case of a roll revert:
> https://v8-roll.appspot.com/
> This only works with a Google account.
> 
> CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;luci.chromium.try:android_optional_gpu_tests_rel
> 
> TBR=hablich@chromium.org,machenbach@chromium.org,kozyatinskiy@chromium.org,sergiyb@chromium.org
> 
> Change-Id: I1c65bbcf6ce40050b917cb288293b9226d1563ab
> Reviewed-on: https://chromium-review.googlesource.com/1049367
> Reviewed-by: v8 autoroll <v8-autoroll@chromium.org>
> Commit-Queue: v8 autoroll <v8-autoroll@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#556739}

TBR=v8-autoroll@chromium.org,machenbach@chromium.org,hablich@chromium.org,kozyatinskiy@chromium.org,sergiyb@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I7108d2aecebef1e7ca0355bca571e85d1cc01499
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;luci.chromium.try:android_optional_gpu_tests_rel
Reviewed-on: https://chromium-review.googlesource.com/1052527
Commit-Queue: Robert Kroeger <rjkroege@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557306}

DEPS

@@ -100,7 +100,7 @@ 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': '9c5f77a1382ee3825f708aba48f5675fb55c84e1',
+  'v8_revision': 'e3f3bcb29041e7e926c0a6542bfb85d98b8667da',
   # 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.