[WIP] refactor: (Part I) make the ownership of URLRequestContextGetter more clear (#13956)

* refactor: desttroy URLRequestContextGetter on IO thread

* Accepts a factory class that can customize the creation of URLRequestContext
* Use a separate request context for media which is derived from the default
* Notify URLRequestContextGetter observers and cleanup on IO thread
* Move most of brightray net/ classes into atom net/

* refactor: remove refs to URLRequestContextGetter on shutdown

* refactor: remove brigtray switches.{cc|h}

* refactor: remove brightray network_delegate.{cc|h}

* refactor: make AtomURLRequestJobFactory the top level factory.

* Allows to use the default handler from content/ for http{s}, ws{s} schemes.
* Removes the storage of job factory in URLRequestContextGetter.

atom/browser/api/atom_api_cookies.h

@@ -10,6 +10,7 @@
 #include "atom/browser/api/trackable_object.h"
 #include "atom/browser/net/cookie_details.h"
 #include "base/callback.h"
+#include "base/callback_list.h"
 #include "native_mate/handle.h"
 #include "net/cookies/canonical_cookie.h"
 
@@ -59,6 +60,8 @@ class Cookies : public mate::TrackableObject<Cookies> {
   void OnCookieChanged(const CookieDetails*);
 
  private:
+  std::unique_ptr<base::CallbackList<void(const CookieDetails*)>::Subscription>
+      cookie_change_subscription_;
   scoped_refptr<AtomBrowserContext> browser_context_;
 
   DISALLOW_COPY_AND_ASSIGN(Cookies);