Add BrowserWindow.capturePage API.

Don't map command to ctrl

We no longer what this behavior because it's confusing unless you
understand that atom-shell does this.

It could happen that we are quitting when the embed thread is still
waiting for the main thread, so we make sure embed thread is always
signaled when quitting.

It's required if we want to include Chromium headers before C headers
and do not break cpplint rules in the meanwhile.

Fix console STDIO