Upgrade to Chrome 40

[zcbenz]

Merge this after there is a stable release of Chrome 40.

[mark-hahn]

Will this fix the webview problem also? Is there an easy way for me to build atom using this so I can test the webview?

[anaisbetts]

@zcbenz Can you git push all your submodules? libchromiumcontent is pinned to a commit that isn't up on GitHub atm

[zcbenz]

Chrome 40 becomes stable today, I'll finish this PR.

@mark-hahn The change I need to fix the <webivew> crash is not in Chrome40 yet, I'm afraid we have to wait until Chrome41, but I'll still have a try.

[zcbenz]

Latest nan is now using NODE_MODULE_VERSION to determine the V8 version to support, in order to be compatible with nan we need to pick a NODE_MODULE_VERSION value very carefully.

[zcbenz]

Currently blocked by compatibility with nan: nodejs/nan#226.

[anaisbetts]

Would it be worth it to forget about the io.js migration for this PR? It seems like it's going to bust a ton of native modules right now since it's super new. Or will Chrome 40's version of V8 bust them anyways, so who cares?

[zcbenz]

The problem is Atom uses lots of native modules and I have to make Atom work with Chrome 40. Anyway I have just uploaded a modified version of nan to work around it.