[Telemetry] Make StartVideoCapture start capturing synchronously.

build/android/pylib/screenshot.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 os
+import tempfile
 import time
 
 import android_commands
 import cmd_helper
 
 
 def _GetTimestamp():
  return time.strftime('%Y-%m-%d-%H%M%S', time.localtime())
 
 
@@ skipping 33 matching lines @@
     rotate: If True, the video will be rotated 90 degrees.
   """
   def __init__(self, adb, host_file, megabits_per_second=4, size=None,
                rotate=False):
     self._adb = adb
     self._device_file = '%s/screen-recording.mp4' % adb.GetExternalStorage()
     self._host_file = host_file or 'screen-recording-%s.mp4' % _GetTimestamp()
     self._host_file = os.path.abspath(self._host_file)
     self._recorder = None
     self._recorder_pids = None
+    self._recorder_stdout = None
+    self._is_started = False
 
     self._args = ['adb']
     if self._adb.GetDevice():
       self._args += ['-s', self._adb.GetDevice()]
-    self._args += ['shell', 'screenrecord']
+    self._args += ['shell', 'screenrecord', '--verbose']
     self._args += ['--bit-rate', str(megabits_per_second * 1000 * 1000)]
     if size:
       self._args += ['--size', '%dx%d' % size]
     if rotate:
       self._args += ['--rotate']
     self._args += [self._device_file]
 
   def Start(self):
     """Start recording video."""
     _EnsureHostDirectory(self._host_file)
-    self._recorder = cmd_helper.Popen(self._args)
+    self._recorder_stdout = tempfile.mkstemp()[1]
+    self._recorder = cmd_helper.Popen(
+        self._args, stdout=open(self._recorder_stdout, 'w'))
     self._recorder_pids = self._adb.ExtractPid('screenrecord')
     if not self._recorder_pids:
       raise RuntimeError('Recording failed. Is your device running Android '
                          'KitKat or later?')
 
+  def IsStarted(self):
+    if not self._is_started:
+      for line in open(self._recorder_stdout):
+        self._is_started = line.startswith('Content area is ')
+        if self._is_started:
+          break
+    return self._is_started
+
   def Stop(self):
     """Stop recording video."""
+    os.remove(self._recorder_stdout)
+    self._is_started = False
     if not self._recorder or not self._recorder_pids:
       return
     self._adb.RunShellCommand('kill -SIGINT ' + ' '.join(self._recorder_pids))
     self._recorder.wait()
 
   def Pull(self):
     """Pull resulting video file from the device.
 
     Returns:
       Output video file name on the host.
     """
     self._adb.PullFileFromDevice(self._device_file, self._host_file)
     self._adb.RunShellCommand('rm -f "%s"' % self._device_file)
     return self._host_file