deps: update V8 to 5.1.281.75

Pick up the latest branch-head for V8 5.1. This branch brings in
improved language support and performance improvements. For full
details: http://v8project.blogspot.com/2016/04/v8-release-51.html

* Picks up the latest branch head for 5.1 [1]
* Edit v8 gitignore to allow trace_event copy
* Update V8 DEP trace_event as per deps/v8/DEPS [2]

[1] https://chromium.googlesource.com/v8/v8.git/+/5.1.281.75
[2] https://chromium.googlesource.com/chromium/src/base/trace_event/common/+/c8c8665

Introduces a semver-minor overload of v8::Function::New() for use
by v8_inspector.

PR-URL: #8054
Refs: #7016
Refs: #7586
Refs: #7615
Reviewed-By: addaleax - Anna Henningsen <anna@addaleax.net>
Reviewed-By: thealphanerd - Myles Borins <myles.borins@gmail.com>
Reviewed-By: mhdawson - Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: evanlucas - Evan Lucas <evanlucas@me.com>
Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>

deps/v8/.ycm_extra_conf.py

@@ -42,7 +42,7 @@
 # Flags from YCM's default config.
 flags = [
 '-DUSE_CLANG_COMPLETER',
-'-std=gnu++0x',
+'-std=gnu++11',
 '-x',
 'c++',
 ]

deps/v8/AUTHORS

@@ -71,6 +71,7 @@ Jianghua Yang <jianghua.yjh@alibaba-inc.com>
 Joel Stanley <joel@jms.id.au>
 Johan Bergström <johan@bergstroem.nu>
 Jonathan Liu <net147@gmail.com>
+Julien Brianceau <jbriance@cisco.com>
 JunHo Seo <sejunho@gmail.com>
 Kang-Hao (Kenny) Lu <kennyluck@csail.mit.edu>
 Karl Skomski <karl@skomski.com>
@@ -87,6 +88,7 @@ Michael Smith <mike@w3.org>
 Mike Gilbert <floppymaster@gmail.com>
 Mike Pennisi <mike@mikepennisi.com>
 Milton Chiang <milton.chiang@mediatek.com>
+Myeong-bo Shim <m0609.shim@samsung.com>
 Nicolas Antonius Ernst Leopold Maria Kaiser <nikai@nikai.net>
 Paolo Giarrusso <p.giarrusso@gmail.com>
 Patrick Gansterer <paroga@paroga.com>