Revert of Migrate DeviceUtils.ReadFile to adb_wrapper

build/android/pylib/flag_changer.py

Index: build/android/pylib/flag_changer.py
diff --git a/build/android/pylib/flag_changer.py b/build/android/pylib/flag_changer.py
index 718bc3971500b2c94dcaa6606ccc0c364de5ae10..c0bcadbe3bd4a9a47d2146b8a428d8dc9188d92a 100644
--- a/build/android/pylib/flag_changer.py
+++ b/build/android/pylib/flag_changer.py
@@ -6,8 +6,6 @@
 
 import pylib.android_commands
 import pylib.device.device_utils
-
-from pylib.device import device_errors
 
 
 class FlagChanger(object):
@@ -34,10 +32,9 @@
     self._cmdline_file = cmdline_file
 
     # Save the original flags.
-    try:
-      self._orig_line = self._device.ReadFile(self._cmdline_file).strip()
-    except device_errors.CommandFailedError:
-      self._orig_line = ''
+    self._orig_line = self._device.ReadFile(self._cmdline_file)
+    if self._orig_line:
+      self._orig_line = self._orig_line[0].strip()
 
     # Parse out the flags into a list to facilitate adding and removing flags.
     self._current_flags = self._TokenizeFlags(self._orig_line)
@@ -107,8 +104,8 @@
       self._device.WriteFile(
           self._cmdline_file, cmd_line, as_root=use_root)
       file_contents = self._device.ReadFile(
-          self._cmdline_file, as_root=use_root).rstrip()
-      assert file_contents == cmd_line, (
+          self._cmdline_file, as_root=use_root)
+      assert len(file_contents) == 1 and file_contents[0] == cmd_line, (
           'Failed to set the command line file at %s' % self._cmdline_file)
     else:
       self._device.RunShellCommand('rm ' + self._cmdline_file,