Update V8 to version 4.3.15.

Summary of changes available at:
https://chromium.googlesource.com/v8/v8/+log/c791d841..155278d6

Please follow these instructions for assigning/CC'ing issues:
https://code.google.com/p/v8-wiki/wiki/TriagingIssues

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/969053002

Cr-Commit-Position: refs/heads/master@{#318755}

DEPS

@@ -47,7 +47,7 @@ vars = {
   # the commit queue can handle CLs rolling Skia
   # and V8 without interference from each other.
   'v8_branch': 'trunk',
-  'v8_revision': '9ed013342d53b0b5a0c3de5380650d0154558891',
+  'v8_revision': '3e7dee100ac4e951719ce264f79a214f6634cf11',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling WebRTC
   # and V8 without interference from each other.