Update V8 to version 6.4.78.

Summary of changes available at:
https://chromium.googlesource.com/v8/v8/+log/18203274..598bc092

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;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel

[email protected],[email protected],[email protected]

Change-Id: I6925034a612649638fad2951ae466be5152a7861
Reviewed-on: https://chromium-review.googlesource.com/732545
Reviewed-by: v8 autoroll <[email protected]>
Commit-Queue: v8 autoroll <[email protected]>
Cr-Commit-Position: refs/heads/master@{#510708}
diff --git a/DEPS b/DEPS
index fa80436..aa64421 100644
--- a/DEPS
+++ b/DEPS
@@ -59,7 +59,7 @@
   # 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': '182032740545159ebdaf5fc9db6aed9b9012c6e4',
+  'v8_revision': '598bc092043cbfa57affb28015463b884ed0a4ab',
   # 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.