[Cronet] Add another method to identify host RNDIS interface

Attempt to ping device via host network interfaces and see if
device's RNDIS network interface's MAC address appears in
host's ARP cache.  This gets this script working on my laptop.

Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester
Change-Id: Ieace3bbd424804824ca5ce5f36e8137598d922b4
Reviewed-on: https://chromium-review.googlesource.com/1112460Reviewed-by: Misha Efimov <mef@chromium.org>
Commit-Queue: Paul Jensen <pauljensen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570737}

components/cronet/android/test/javaperftests/android_rndis_forwarder.py

@@ -130,6 +130,7 @@ class AndroidRndisConfigurator(object):
   _NETWORK_INTERFACES = '/etc/network/interfaces'
   _INTERFACES_INCLUDE = 'source /etc/network/interfaces.d/*.conf'
   _TELEMETRY_INTERFACE_FILE = '/etc/network/interfaces.d/telemetry-{}.conf'
+  _DEVICE_IP_ADDRESS = '192.168.123.2'
 
   def __init__(self, device):
     self._device = device
@@ -173,6 +174,12 @@ class AndroidRndisConfigurator(object):
       assert len(candidates) == 1, 'Found more than one rndis device!'
       return candidates[0]
 
+  def _FindDeviceRndisMacAddress(self, interface):
+    """Returns the MAC address of the RNDIS network interface if present."""
+    config = self._device.RunShellCommand(
+        ['ip', '-o', 'link', 'show', interface], check_return=True)[0]
+    return config.split('link/ether ')[1][:17]
+
   def _EnumerateHostInterfaces(self):
     host_platform = platform.GetHostPlatform().GetOSName()
     if host_platform == 'linux':
@@ -181,7 +188,7 @@ class AndroidRndisConfigurator(object):
       return subprocess.check_output(['ifconfig']).splitlines()
     raise NotImplementedError('Platform %s not supported!' % host_platform)
 
-  def _FindHostRndisInterface(self):
+  def _FindHostRndisInterface(self, device_mac_address):
     """Returns the name of the host-side network interface."""
     interface_list = self._EnumerateHostInterfaces()
     ether_address = self._device.ReadFile(
@@ -191,6 +198,15 @@ class AndroidRndisConfigurator(object):
     for line in interface_list:
       if not line.startswith((' ', '\t')):
         interface_name = line.split(':')[-2].strip()
+        # Attempt to ping device to trigger ARP for device.
+        with open(os.devnull, 'wb') as devnull:
+          subprocess.call(['ping', '-w1', '-c1', '-I', interface_name,
+              self._DEVICE_IP_ADDRESS], stdout=devnull, stderr=devnull)
+        # Check if ARP cache now has device in it.
+        arp = subprocess.check_output(
+            ['arp', '-i', interface_name, self._DEVICE_IP_ADDRESS])
+        if device_mac_address in arp:
+          return interface_name
       elif ether_address in line:
         return interface_name
       # NOTE(pauljensen): |ether_address| seems incorrect on Nougat devices,
@@ -266,13 +282,15 @@ function doit() {
   # For some combinations of devices and host kernels, adb won't work unless the
   # interface is up, but if we bring it up immediately, it will break adb.
   #sleep 1
-  ifconfig rndis0 192.168.123.2 netmask 255.255.255.0 up
+  ifconfig rndis0 %(device_ip_address)s netmask 255.255.255.0 up
   echo DONE >> %(prefix)s.log
 }
 
 doit &
-    """ % {'dev': self._RNDIS_DEVICE, 'functions': 'rndis,adb',
-           'prefix': script_prefix}
+    """ % {'dev': self._RNDIS_DEVICE,
+           'functions': 'rndis,adb',
+           'prefix': script_prefix,
+           'device_ip_address': self._DEVICE_IP_ADDRESS}
     script_file = '%s.sh' % script_prefix
     log_file = '%s.log' % script_prefix
     self._device.WriteFile(script_file, script)
@@ -295,7 +313,8 @@ doit &
       if not force:
         device_iface = self._FindDeviceRndisInterface()
         if device_iface:
-          host_iface = self._FindHostRndisInterface()
+          device_mac_address = self._FindDeviceRndisMacAddress(device_iface)
+          host_iface = self._FindHostRndisInterface(device_mac_address)
           if host_iface:
             return device_iface, host_iface
       self._DisableRndis()