Update usb charging command to wait for it to succeed.

build/android/pylib/android_commands.py

Index: build/android/pylib/android_commands.py
diff --git a/build/android/pylib/android_commands.py b/build/android/pylib/android_commands.py
index 8faa1be4f860d4f779ee4743404b78dc9973cb96..21dd379d8672f7831ee991c6fe13b5c1bf521347 100644
--- a/build/android/pylib/android_commands.py
+++ b/build/android/pylib/android_commands.py
@@ -1870,14 +1870,30 @@ class AndroidCommands(object):
     if not command:
       raise Exception('Unable to act on usb charging.')
     disable_command = command['disable_command']
-    self.RunShellCommand(disable_command)
+    # Do not loop directly on self.IsDeviceCharging to cut the number of calls
+    # to the device.
+    while True:
+      self.RunShellCommand(disable_command)
+      if not self.IsDeviceCharging():
+        break
 
   def EnableUsbCharging(self):
     command = self._GetControlUsbChargingCommand()
     if not command:
       raise Exception('Unable to act on usb charging.')
     disable_command = command['enable_command']
-    self.RunShellCommand(disable_command)
+    # Do not loop directly on self.IsDeviceCharging to cut the number of calls
+    # to the device.
+    while True:
+      self.RunShellCommand(disable_command)
+      if self.IsDeviceCharging():
+        break
+
+  def IsDeviceCharging(self):
+    for line in self.RunShellCommand('dumpsys battery'):
+      if 'powered: ' in line:
+        if line.split('powered: ')[1] == 'true':
+          return True
 
 
 class NewLineNormalizer(object):