shill: cellular: simplify property change notification

Simplify property change notification by using a single mechanism to
handle it instead of two.  Old style notifications are turned into new
style notifications by the modem object.

A few minor style clean ups -- remove std:: where not needed and
ensure that public interfaces are declared as public interfaces in
subclasses (i.e not protected).

BUG=chromium-os:29569
TEST=run unit tests

Change-Id: If8b957d8b6518c95fa1d20bdef7d1ec6a8ed5ea3
Reviewed-on: https://gerrit.chromium.org/gerrit/20395
Tested-by: Jason Glasgow <jglasgow@chromium.org>
Reviewed-by: Nathan J. Williams <njw@chromium.org>
Commit-Ready: Jason Glasgow <jglasgow@chromium.org>
diff --git a/modem.h b/modem.h
index 92789ff..a735f22 100644
--- a/modem.h
+++ b/modem.h
@@ -80,6 +80,8 @@
       uint32 input) const = 0;
   virtual bool GetLinkName(const DBusPropertiesMap &properties,
                            std::string *name) const = 0;
+  // Returns the name of the DBUS Modem interface.
+  virtual std::string GetModemInterface(void) const = 0;
 
  private:
   friend class ModemTest;
@@ -150,6 +152,7 @@
       uint32 input) const;
   virtual bool GetLinkName(const DBusPropertiesMap &modem_properties,
                            std::string *name) const;
+  virtual std::string GetModemInterface(void) const;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ModemClassic);
@@ -174,6 +177,7 @@
       uint32 input) const;
   virtual bool GetLinkName(const DBusPropertiesMap &modem_properties,
                            std::string *name) const;
+  virtual std::string GetModemInterface(void) const;
 
  private:
   friend class Modem1Test;