Add --proxy-server and --no-proxy-server switches.
linux: Suppress test for "enable-larger-than-screen".

It is failing on some DEs.
Make process.activateUvLoop friendly to multi-context, fixes #587.
Avoid calling GetRequestContext() in UI thread, fixes #591.

Since we can access job factory without touching the request context,
there is no need to make sure GetRequestContext() is called before using
the protocol module.
Upgrade brightray for new URLRequestContextGetter interface.
Bump v0.15.9.
make CI build faster
Merge pull request #594 from PeterDaveHello/patch-1

make CI build faster
linux: Add "dark-theme" option for BrowserWindow, fixes #352.
No more need to flip rect for capturePage, fixes #589.
Add printing related source codes from chrome.
Initialize the fake BrowserProcess object.
Fix compiling with print messages.
Allow script initialized window.print().
Upgrade libchromiumcontent to contain printing headers.
Fix cpplint warnings.
Initailize PrintViewManagerBasic for browser window.
Add BrowserWindow.print() method.
Setup PrintingMessageFilter for printing.
Strip out print preview.