[Android] Add record functionality to logcat monitor.

build/android/devil/utils/cmd_helper.py

 # Copyright (c) 2012 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.
 
 """A wrapper for subprocess to make calling shell commands easier."""
 
 import logging
 import os
 import pipes
 import select
@@ skipping 291 matching lines @@
     buffer_output += data
     has_incomplete_line = buffer_output[-1] not in '\r\n'
     lines = buffer_output.splitlines()
     buffer_output = lines.pop() if has_incomplete_line else ''
     for line in lines:
       yield line
   if buffer_output:
     yield buffer_output
   if check_status and process.returncode:
     raise subprocess.CalledProcessError(process.returncode, cmd)
+
+
+def IterCmdOutput(args, timeout=None, cwd=None, shell=False,

[mikecase (-- gone --), 2015/12/16 23:52:05]

Need the logcat output as soon as I can get it to make the logcat monitor work
better.

Getting it line by line causes trouble if you log something to the device and
then instantly call FindAll() or something. Sometimes the logcat monitor hasnt
processed enough lines in time.

+                  check_status=True):
+  """Executes a subprocess and continuously yields its output.
+
+  Args:
+    args: List of arguments to the program, the program to execute is the first
+      element.
+    cwd: If not None, the subprocess's current directory will be changed to
+      |cwd| before it's executed.
+    shell: Whether to execute args as a shell command. Must be True if args
+      is a string and False if args is a sequence.
+    check_status: A boolean indicating whether to check the exit status of the
+      process after all output has been read.
+
+  Yields:
+    The output of the subprocess.
+
+  Raises:
+    CalledProcessError if check_status is True and the process exited with a
+      non-zero exit status.
+  """
+  cmd = _ValidateAndLogCommand(args, cwd, shell)
+  process = Popen(args, cwd=cwd, shell=shell, stdout=subprocess.PIPE,
+                  stderr=subprocess.STDOUT)
+  for data in _IterProcessStdout(process, timeout=timeout):
+    yield data
+  if check_status and process.returncode:
+    raise subprocess.CalledProcessError(process.returncode, cmd)