Update V8 to version 7.0.125.

Summary of changes available at:
https://chromium.googlesource.com/v8/v8/+log/b538ae75..0a9c4581

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,v8-waterfall-sheriff@grotations.appspotmail.com

Change-Id: Iae796f0d9518546f07df16676e98e0f8d3fec652
Reviewed-on: https://chromium-review.googlesource.com/1158803Reviewed-by: V8 Autoroller <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Commit-Queue: V8 Autoroller <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#579940}

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': 'b538ae754652e0cbe2d852dcfd35eeba4ff45f7b',
+  'v8_revision': '0a9c45817264dfb25a999f35df0f638e979d74e2',
   # 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.