[Android] Add LogcatMonitor.

build/android/pylib/device/adb_wrapper.py

Index: build/android/pylib/device/adb_wrapper.py
diff --git a/build/android/pylib/device/adb_wrapper.py b/build/android/pylib/device/adb_wrapper.py
index 1dbb1d89a9a2a8b7d04b007b47d4c7f20845af5a..7d11671212d236fcb9a4d6a7dc738775ef93d29f 100644
--- a/build/android/pylib/device/adb_wrapper.py
+++ b/build/android/pylib/device/adb_wrapper.py
@@ -285,7 +285,8 @@ class AdbWrapper(object):
           cmd, 'path does not specify an accessible directory in the device',
           device_serial=self._device_serial)
 
-  def Logcat(self, filter_spec=None, timeout=None):
+  def Logcat(self, clear=False, dump=False, filter_spec=None,
+             logcat_format=None, timeout=None):
     """Get an iterator over the logcat output.
 
     Args:
@@ -296,6 +297,12 @@ class AdbWrapper(object):
       logcat output line by line.
     """
     cmd = ['logcat']
+    if clear:
+      cmd.append('-c')
+    if dump:
+      cmd.append('-d')
+    if logcat_format:
+      cmd.extend(['-v', logcat_format])
     if filter_spec is not None:
       cmd.append(filter_spec)
     return self._IterRunDeviceAdbCmd(cmd, timeout)