[Mac] Move MessagePump CrAppProtocol dependency to setup.

[Superseded by another CL.]

[Mac] Move MessagePump CrAppProtocol dependency to setup.

Pull the CrAppProtocol autorelease-pool handling down into
MessagePumpCrApplication, which is selected at Create() if NSApp
implements the right protocol.  UsingCrApp() allows clients to
confirm the correct setup (unfortunately, synchronizing NSApp
initialization and MessagePump::Create() would be intrusive).

Also push CrAppProtocol and CrAppControlProtocol implementation
up into BrowserCrApplication, and reparent that class from
NSApplication.  With this change, the following implementations
can be removed or changed:
 - CrDrtApplication removed from DRT.
 - ServiceCrApplication reparented to NSApplication.
 - Remove CrApplication registration from gpu, plugin, and renderer mains.
 - MockCrApp dependency from remoting sample code
 - content/common/chrome_application_mac*
Those changes intentionally left to another CL to reduce bickering.

BUG=102224