Create AndroidCommandLineBackend to handle setting up cmdline args

tools/telemetry/telemetry/core/backends/android_command_line_backend.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 pipes
+import sys
+
+from telemetry.core import util
+
+util.AddDirToPythonPath(util.GetChromiumSrcDir(), 'build', 'android')
+from pylib.device import device_errors  # pylint: disable=F0401
+
+
+def QuoteIfNeeded(arg):

[nednguyen, 2015/01/13 16:03:04]

Please make this private & add unittest for it.

[ariblue, 2015/01/13 20:23:37]

Done.

+  # Properly escape "key=valueA valueB" to "key='valueA valueB'"
+  # Values without spaces, or that seem to be quoted are left untouched.
+  # This is required so CommandLine.java can parse valueB correctly rather
+  # than as a separate switch.
+  params = arg.split('=', 1)
+  if len(params) != 2:
+    return arg
+  key, values = params
+  if ' ' not in values:
+    return arg
+  if values[0] in '"\'' and values[-1] == values[0]:
+    return arg
+  return '%s=%s' % (key, pipes.quote(values))
+
+
+class AndroidCommandLineBackend(object):
+

[nednguyen, 2015/01/13 16:03:04]

Can you add pydoc for this class?

[ariblue, 2015/01/13 20:23:37]

Done.

+  def __init__(self, adb, backend_settings, startup_args):
+    self._adb = adb
+    self._backend_settings = backend_settings
+    self._startup_args = startup_args
+    self._saved_command_line_file_contents = ''
+
+  @property
+  def command_line_file(self):
+    return self._backend_settings.GetCommandLineFile(self._adb.IsUserBuild())
+
+  def SetUpCommandLine(self):
+    args = [self._backend_settings.pseudo_exec_name]
+    args.extend(self._startup_args)
+    content = ' '.join(QuoteIfNeeded(arg) for arg in args)
+
+    try:
+      # Save the current command line to restore later, except if it appears to
+      # be a  Telemetry created one. This is to prevent a common bug where
+      # --host-resolver-rules borks people's browsers if something goes wrong
+      # with Telemetry.
+      self._saved_command_line_file_contents = ''.join(self._ReadFile())
+      if '--host-resolver-rules' in self._saved_command_line_file_contents:
+        self._saved_command_line_file_contents = ''
+      self._WriteFile(content)
+    except device_errors.CommandFailedError:
+      logging.critical('Cannot set Chrome command line. '
+                       'Fix this by flashing to a userdebug build.')
+      sys.exit(1)
+
+  def RestoreCommandLine(self):
+    self._WriteFile(self._saved_command_line_file_contents)
+
+  def _ReadFile(self):
+    return self._adb.device().ReadFile(self.command_line_file)
+
+  def _WriteFile(self, contents):
+    self._adb.device().WriteFile(self.command_line_file, contents, as_root=True)