Update from https://crrev.com/308331

build/android/pylib/device/adb_wrapper.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.
 
 """This module wraps Android's adb tool.
 
 This is a thin wrapper around the adb interface. Any additional complexity
 should be delegated to a higher level (ex. DeviceUtils).
 """
 
@@ skipping 38 matching lines @@
 
     Args:
       device_serial: The device serial number as a string.
     """
     if not device_serial:
       raise ValueError('A device serial must be specified')
     self._device_serial = str(device_serial)
 
   # pylint: disable=unused-argument
   @classmethod
+  def _BuildAdbCmd(cls, args, device_serial):
+    cmd = [constants.GetAdbPath()]
+    if device_serial is not None:
+      cmd.extend(['-s', device_serial])
+    cmd.extend(args)
+    return cmd
+  # pylint: enable=unused-argument
+
+  # pylint: disable=unused-argument
+  @classmethod
   @decorators.WithTimeoutAndRetries
   def _RunAdbCmd(cls, args, timeout=None, retries=None, device_serial=None,
                  check_error=True):
-    cmd = [constants.GetAdbPath()]
-    if device_serial is not None:
-      cmd.extend(['-s', device_serial])
-    cmd.extend(args)
     status, output = cmd_helper.GetCmdStatusAndOutputWithTimeout(
-        cmd, timeout_retry.CurrentTimeoutThread().GetRemainingTime())
+        cls._BuildAdbCmd(args, device_serial),
+        timeout_retry.CurrentTimeoutThread().GetRemainingTime())
     if status != 0:
       raise device_errors.AdbCommandFailedError(
           args, output, status, device_serial)
     # This catches some errors, including when the device drops offline;
     # unfortunately adb is very inconsistent with error reporting so many
     # command failures present differently.
     if check_error and output.startswith('error:'):
       raise device_errors.AdbCommandFailedError(args, output)
     return output
   # pylint: enable=unused-argument
 
   def _RunDeviceAdbCmd(self, args, timeout, retries, check_error=True):
     """Runs an adb command on the device associated with this object.
 
     Args:
       args: A list of arguments to adb.
       timeout: Timeout in seconds.
       retries: Number of retries.
       check_error: Check that the command doesn't return an error message. This
         does NOT check the exit status of shell commands.
 
     Returns:
       The output of the command.
     """
     return self._RunAdbCmd(args, timeout=timeout, retries=retries,
                            device_serial=self._device_serial,
                            check_error=check_error)
 
+  def _IterRunDeviceAdbCmd(self, args, timeout):
+    """Runs an adb command and returns an iterator over its output lines.
+
+    Args:
+      args: A list of arguments to adb.
+      timeout: Timeout in seconds.
+
+    Yields:
+      The output of the command line by line.
+    """
+    return cmd_helper.IterCmdOutputLines(
+      self._BuildAdbCmd(args, self._device_serial), timeout=timeout)
+
   def __eq__(self, other):
     """Consider instances equal if they refer to the same device.
 
     Args:
       other: The instance to compare equality with.
 
     Returns:
       True if the instances are considered equal, false otherwise.
     """
     return self._device_serial == str(other)
@@ skipping 129 matching lines @@
     cmd = ['ls', path]
     lines = self._RunDeviceAdbCmd(
         cmd, timeout=timeout, retries=retries).splitlines()
     if lines:
       return [ParseLine(line) for line in lines]
     else:
       raise device_errors.AdbCommandFailedError(
           cmd, 'path does not specify an accessible directory in the device',
           device_serial=self._device_serial)
 
-  def Logcat(self, filter_spec=None, timeout=_DEFAULT_TIMEOUT,
-             retries=_DEFAULT_RETRIES):
-    """Get the logcat output.
+  def Logcat(self, filter_spec=None, timeout=None):
+    """Get an iterator over the logcat output.
 
     Args:
       filter_spec: (optional) Spec to filter the logcat.
       timeout: (optional) Timeout per try in seconds.
-      retries: (optional) Number of retries to attempt.
 
-    Returns:
-      logcat output as a string.
+    Yields:
+      logcat output line by line.
     """
     cmd = ['logcat']
     if filter_spec is not None:
       cmd.append(filter_spec)
-    return self._RunDeviceAdbCmd(cmd, timeout, retries, check_error=False)
+    return self._IterRunDeviceAdbCmd(cmd, timeout)
 
   def Forward(self, local, remote, timeout=_DEFAULT_TIMEOUT,
               retries=_DEFAULT_RETRIES):
     """Forward socket connections from the local socket to the remote socket.
 
     Sockets are specified by one of:
       tcp:<port>
       localabstract:<unix domain socket name>
       localreserved:<unix domain socket name>
       localfilesystem:<unix domain socket name>
@@ skipping 167 matching lines @@
     """Restarts the adbd daemon with root permissions, if possible.
 
     Args:
       timeout: (optional) Timeout per try in seconds.
       retries: (optional) Number of retries to attempt.
     """
     output = self._RunDeviceAdbCmd(['root'], timeout, retries)
     if 'cannot' in output:
       raise device_errors.AdbCommandFailedError(
           ['root'], output, device_serial=self._device_serial)