Factor out a system_properties interface for interacting with getprop/setprop.

tools/telemetry/telemetry/core/backends/android_rndis.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 import logging
 import os
 import re
 import socket
 import struct
 import subprocess
 import sys
@@ skipping 95 matching lines @@
       if not line.startswith(' '):
         interface_name = line.split()[1].strip(':')
       elif ether_address in line:
         return interface_name
 
   def _WriteProtectedFile(self, path, contents):
     subprocess.check_call(
         ['sudo', 'bash', '-c', 'echo -e "%s" > %s' % (contents, path)])
 
   def _DisableRndis(self):
-    self._adb.RunShellCommand('setprop sys.usb.config adb')
+    self._adb.system_properties['sys.usb.config'] = 'adb'
     self._WaitForDevice()
 
   def _EnableRndis(self):
     """Enables the RNDIS network interface."""
     script_prefix = '/data/local/tmp/rndis'
     # This could be accomplished via "svc usb setFunction rndis" but only on
     # devices which have the "USB tethering" feature.
     # Also, on some devices, it's necessary to go through "none" function.
     script = """
 trap '' HUP
@@ skipping 192 matching lines @@
       force = True
     raise Exception('No connectivity, giving up.')
 
   def _GetCurrentDns(self):
     """Returns current gateway, dns1, and dns2."""
     routes = self._adb.RunShellCommand('cat /proc/net/route')[1:]
     routes = [route.split() for route in routes]
     default_routes = [route[0] for route in routes if route[1] == '00000000']
     return (
       default_routes[0] if default_routes else None,
-      self._adb.RunShellCommand('getprop net.dns1')[0],
-      self._adb.RunShellCommand('getprop net.dns2')[0],
+      self._adb.system_properties['net.dns1'],
+      self._adb.system_properties['net.dns2'],
     )
 
   def _OverrideDns(self, iface, dns1, dns2):
     """Overrides device's DNS configuration.
 
     Args:
       iface: name of the network interface to make default
       dns1, dns2: nameserver IP addresses
     """
     if not iface:
       return  # If there is no route, then nobody cares about DNS.
     # DNS proxy in older versions of Android is configured via properties.
     # TODO(szym): run via su -c if necessary.
-    self._adb.RunShellCommand('setprop net.dns1 ' + dns1)
-    self._adb.RunShellCommand('setprop net.dns2 ' + dns2)
-    dnschange = self._adb.RunShellCommand('getprop net.dnschange')[0]
+    self._adb.system_properties['net.dns1'] = dns1
+    self._adb.system_properties['net.dns2'] = dns2
+    dnschange = self._adb.system_properties['net.dnschange']
     if dnschange:
-      self._adb.RunShellCommand('setprop net.dnschange %s' %
-                                (int(dnschange) + 1))
+      self._adb.system_properties['net.dnschange'] = int(dnschange) + 1
     # Since commit 8b47b3601f82f299bb8c135af0639b72b67230e6 to frameworks/base
     # the net.dns1 properties have been replaced with explicit commands for netd
     self._adb.RunShellCommand('ndc netd resolver setifdns %s %s %s' %
                               (iface, dns1, dns2))
     # TODO(szym): if we know the package UID, we could setifaceforuidrange
     self._adb.RunShellCommand('ndc netd resolver setdefaultif %s' % iface)
 
   @property
   def host_ip(self):
     return self._host_ip
 
   @property
   def url(self):
     # localhost and domains which resolve on the host's private network will not
     # be resolved by the DNS proxy to the HTTP proxy.
     return 'http://%s:%d' % (self._host_ip, self._host_port)
 
   def Close(self):
     self._OverrideDns(*self._original_dns)
     self._DisableRndis()