Add instance-level in-memory cache for PushIfNeeded().

This speeds up PushIfNeeded() execution times on a same instance of
AndroidCommands for repetitive files. This can be achieved by mapping host file
paths to their mtime at push time as tonyg@ pointed out although this assumes
that the device doesn't modify the files.

This is needed to make PurgeUnpinnedAshmem() reasonably fast to execute in
Telemetry. This CL decreases by 40 secs the execution time of netsim.top_10
whem memory is measured for each page (and PurgeUnpinnedAshmem() is called
before each measurement).

BUG=323494,326929
R=bulach@chromium.org, craigdh@chromium.org, tonyg@chromium.org

Review URL: https://codereview.chromium.org/97133002

git-svn-id: http://src.chromium.org/svn/trunk/src/build@239757 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/pylib/android_commands.py

@@ -260,6 +260,7 @@ class AndroidCommands(object):
     self._util_wrapper = ''
     self._api_strict_mode = api_strict_mode
     self._system_properties = system_properties.SystemProperties(self.Adb())
+    self._push_if_needed_cache = {}
 
     if not self._api_strict_mode:
       logging.warning(
@@ -965,6 +966,15 @@ class AndroidCommands(object):
     MAX_INDIVIDUAL_PUSHES = 50
     assert os.path.exists(host_path), 'Local path not found %s' % host_path
 
+    # See if the file on the host changed since the last push (if any) and
+    # return early if it didn't. Note that this shortcut assumes that the tests
+    # on the device don't modify the files.
+    if not os.path.isdir(host_path):
+      if host_path in self._push_if_needed_cache:
+        host_path_mtime = self._push_if_needed_cache[host_path]
+        if host_path_mtime == os.stat(host_path).st_mtime:
+          return
+
     def GetHostSize(path):
       return int(cmd_helper.GetCmdOutput(['du', '-sb', path]).split()[0])
 
@@ -989,6 +999,8 @@ class AndroidCommands(object):
       while True:
         output = self._adb.SendCommand(push_command, timeout_time=30 * 60)
         if _HasAdbPushSucceeded(output):
+          if not os.path.isdir(host_path):
+            self._push_if_needed_cache[host] = os.stat(host).st_mtime
           return
         if retry < 3:
           retry += 1