shill: Delay cellular device creation if DeviceInfo is not available yet.

DeviceInfo notifies ModemInfo/ModemManager/Modem whenever a new cellular device
link is added so that cellular devices can be constructed and registered. This
fixes the current behavior where the device is not created at all if its device
info is not available yet.

BUG=chromium-os:24855
TEST=tested on device

Change-Id: I929bd70a6692a9ec6c66f51e01e44fca4433eb87
Reviewed-on: https://gerrit.chromium.org/gerrit/13866
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Reviewed-by: Eric Shienbrood <ers@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/manager.h b/manager.h
index dd62b83..6f77c63 100644
--- a/manager.h
+++ b/manager.h
@@ -100,6 +100,7 @@
   void PopAnyProfile(Error *error);
 
   virtual DeviceInfo *device_info() { return &device_info_; }
+  ModemInfo *modem_info() { return &modem_info_; }
   PropertyStore *mutable_store() { return &store_; }
   virtual const PropertyStore &store() const { return store_; }