Don't push md5sum every time it is used.

build/android/pylib/android_commands.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.
 
 """Provides an interface to communicate with the device via the adb command.
 
 Assumes adb binary is currently on system path.
 """
 # pylint: disable-all
 
@@ skipping 964 matching lines @@
       host_path: Path (file or directory) on the host.
       device_path: Path on the device.
 
     Returns:
       A tuple containing lists of the host and device md5sum results as
       created by _ParseMd5SumOutput().
     """
     md5sum_dist_path = os.path.join(constants.GetOutDirectory(),
                                     'md5sum_dist')
     assert os.path.exists(md5sum_dist_path), 'Please build md5sum.'
-    command = 'push %s %s' % (md5sum_dist_path, MD5SUM_DEVICE_FOLDER)
-    assert _HasAdbPushSucceeded(self._adb.SendCommand(command))
+    md5sum_dist_mtime = os.stat(md5sum_dist_path).st_mtime
+    if (md5sum_dist_path not in self._push_if_needed_cache or
+        self._push_if_needed_cache[md5sum_dist_path] != md5sum_dist_mtime):
+      command = 'push %s %s' % (md5sum_dist_path, MD5SUM_DEVICE_FOLDER)
+      assert _HasAdbPushSucceeded(self._adb.SendCommand(command))
+      self._push_if_needed_cache[md5sum_dist_path] = md5sum_dist_mtime
 
     (_, md5_device_output) = self.GetAndroidToolStatusAndOutput(
         self._util_wrapper + ' ' + MD5SUM_DEVICE_PATH + ' ' + device_path,
         lib_path=MD5SUM_DEVICE_FOLDER,
         timeout_time=2 * 60)
     device_hash_tuples = _ParseMd5SumOutput(md5_device_output)
     assert os.path.exists(host_path), 'Local path not found %s' % host_path
     md5sum_output = cmd_helper.GetCmdOutput(
         [os.path.join(constants.GetOutDirectory(), 'md5sum_bin_host'),
          host_path])
@@ skipping 980 matching lines @@
   """
   def __init__(self, output):
     self._output = output
 
   def write(self, data):
     data = data.replace('\r\r\n', '\n')
     self._output.write(data)
 
   def flush(self):
     self._output.flush()