shill: Broadcast service strength changes.

Similar to flimflam, make strength a property of the base service class, and
broadcast changes to the property.

BUG=chromium-os:25011
TEST=unit tests, tested on device

Change-Id: Iff7a638a2c1b8a828260739273c428373aff420e
Reviewed-on: https://gerrit.chromium.org/gerrit/14054
Commit-Ready: Darin Petkov <petkov@chromium.org>
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Darin Petkov <petkov@chromium.org>
diff --git a/adaptor_interfaces.h b/adaptor_interfaces.h
index 70098fe..8f4d8d2 100644
--- a/adaptor_interfaces.h
+++ b/adaptor_interfaces.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -109,6 +109,7 @@
   virtual void UpdateConnected() = 0;
 
   virtual void EmitBoolChanged(const std::string &name, bool value) = 0;
+  virtual void EmitUint8Changed(const std::string &name, uint8 value) = 0;
   virtual void EmitUintChanged(const std::string &name, uint32 value) = 0;
   virtual void EmitIntChanged(const std::string &name, int value) = 0;
   virtual void EmitStringChanged(const std::string &name,