Merge to XFA: Add signatures to FXJS_V8.

(cherry picked from commit 158e335717efba9dce3aa6f6d1e31ed884e1f59e)
Original Review URL: https://codereview.chromium.org/1353193004 .

TBR=jochen@chromium.org, krasin@google.com

Review URL: https://codereview.chromium.org/1376343002 .
3 files changed