restarting adb server before each testing start will cause conflict for multiple emulators

build/android/emulator.py

Index: build/android/emulator.py
diff --git a/build/android/emulator.py b/build/android/emulator.py
index d4f3caa409272f35f97022e1bf099f20ea08cc77..0d7c96b610df03940e42c9897487c5e26ffae582 100755
--- a/build/android/emulator.py
+++ b/build/android/emulator.py
@@ -52,6 +52,22 @@ def _KillAllEmulators():
     time.sleep(1)
 
 
+def DeleteAllTempAVDs():
+  """Delete all temporary AVDs which are created for tests.
+
+  If the test exits abnormally and some temporary AVDs created when testing may
+  be left in the system. Clean these AVDs.
+  """
+  avds = android_commands.GetAVDs()
+  if not avds:
+    return
+  for avd_name in avds:
+    if 'run_tests_avd' in avd_name:
+      cmd = ['android', '-s', 'delete', 'avd', '--name', avd_name]
+      cmd_helper.GetCmdOutput(cmd)
+      logging.info('Delete AVD %s' % avd_name)
+
+
 class PortPool(object):
   """Pool for emulator port starting position that changes over time."""
   _port_min = 5554
@@ -149,6 +165,10 @@ class Emulator(object):
     return ('emulator-%d' % port, port)
 
   def _CreateAVD(self, avd_name):
+    """Creates an AVD with the given name.
+
+    Return avd_name.
+    """
     avd_command = [
         self.android,
         '--silent',
@@ -166,9 +186,10 @@ class Emulator(object):
     avd_process.stdin.write('no\n')
     avd_process.wait()
     logging.info('Create AVD command: %s', ' '.join(avd_command))
-    return self.avd
+    return avd_name
 
   def _DeleteAVD(self):
+    """Delete the AVD of this emulator."""
     avd_command = [
         self.android,
         '--silent',