Changes the primordial browser process service manager connection
to identify as a singleton service named content_packaged_services.
This is used to package any existing global services previously
associated with the global root content_browser connection.

The root content_browser connection still exists in order to serve
as a client process host for non-renderer child processes.

One result of this change is that no services other than content_*
are allowed to connect directly to content_browser, in order to avoid
racing with the (now asynchronous) content_browser instance creation
by ServiceManagerContext. As such, code which previously connected to
content_browser has also been fixed to do something less weird. To wit:

 - An "ash" service is now embedded in the browser process when not
   running in mash mode - this allows simplification of ash client code
   as there is no longer a need to switch the target service name at
   runtime when connecting to ash interfaces
 - A new "chrome" service is packaged in content_packaged_services by
   within Chrome. This hosts a mash::mojom::Launchable interface, allowing
   Chrome to be launched within mash by connecting to "chrome"
 - ChromeInterfaceFactory is deleted

Somewhat unrelated but because this CL exposed a timing issue between packaged
service connection and main thread browser initialization, this also removes the
unnecessary blocking of startup on service manager connection (see change in
chrome_browser_main_extra_parts_views.cc.)

BUG=649407,594852
TEST=chrome --mash functions normally, standalone mash runner functions normally with chrome, chrome non-mash functions normally, browser_tests work with and without --run-in-mash
TBR=tsepez@chromium.org

Review-Url: https://codereview.chromium.org/2695803004
Cr-Commit-Position: refs/heads/master@{#450750}