Update V8 to version 7.6.15.

Summary of changes available at:
https://chromium.googlesource.com/v8/v8/+log/54c8fd37..99694fa3

Please follow these instructions for assigning/CC'ing issues:
https://v8.dev/docs/triage-issues

Please close rolling in case of a roll revert:
https://v8-roll.appspot.com/
This only works with a Google account.

CQ_INCLUDE_TRYBOTS=luci.chromium.try:linux-blink-rel
CQ_INCLUDE_TRYBOTS=luci.chromium.try:linux_optional_gpu_tests_rel
CQ_INCLUDE_TRYBOTS=luci.chromium.try:mac_optional_gpu_tests_rel
CQ_INCLUDE_TRYBOTS=luci.chromium.try:win_optional_gpu_tests_rel
CQ_INCLUDE_TRYBOTS=luci.chromium.try:android_optional_gpu_tests_rel

TBR=hablich@chromium.org,v8-waterfall-sheriff@grotations.appspotmail.com

Change-Id: Id98ad87edf32963e8e359b07f99a94242a6abb3c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1580644Reviewed-by: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Commit-Queue: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#653540}

DEPS

@@ -133,7 +133,7 @@ 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': '54c8fd3707de753c47889cd0f395859a9df6a226',
+  'v8_revision': '99694fa360eebc7bd8fa7eb1e7474931232dc5d3',
   # 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.