[shill] Enable default profile to persist device info

Make Profile::Save() take a pointer to a vector of DeviceRefPtrs.  The base
implementation ignores this pointer, but the DefaultProfile implementation
persists all the devices to disk.

BUG=chromium-os:17254
TEST=unit
STATUS=Verified

Change-Id: I5d72bd2319edfb9ae57366cbd5c766b558ffc8a4
Reviewed-on: http://gerrit.chromium.org/gerrit/8057
Commit-Ready: Chris Masone <cmasone@chromium.org>
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: Darin Petkov <petkov@chromium.org>
diff --git a/device.h b/device.h
index 0ab72a9..7574e4e 100644
--- a/device.h
+++ b/device.h
@@ -97,7 +97,7 @@
   RTNLHandler *rtnl_handler() { return rtnl_handler_; }
 
   bool Load(StoreInterface *storage);
-  bool Save(StoreInterface *storage);
+  virtual bool Save(StoreInterface *storage);
 
   void set_dhcp_provider(DHCPProvider *provider) { dhcp_provider_ = provider; }