Update V8 to version 4.4.31.

Summary of changes available at:
https://chromium.googlesource.com/v8/v8/+log/e2ee9248..18297c96

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

TBR=hablich@chromium.org,machenbach@chromium.org,yangguo@chromium.org,vogelheim@chromium.org

Review URL: https://codereview.chromium.org/1096743004

Cr-Commit-Position: refs/heads/master@{#326751}

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': 'e2ee9248e7c7b2a5a2f919f593290478b5905bb7',
+  'v8_revision': '18297c963797cd962eb9c1e78855b7125727cb6c',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling WebRTC
   # and V8 without interference from each other.