emulator: wait for decryption to complete during avd create

Android devices with full-disk encryption will be encrypted on first boot,
and then get decrypted to continue the boot process.
Wait for this step to complete otherwise the avd may have
"Encryption Unsuccessful" error.

Also add debug tag "init" for avd create to print more debug message

Need crrev.com/c/2153811 to land first

Bug: 922145, 1057811
Change-Id: I2037d8f6a7f8edfa83e276e7ef94b93bebbb83ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2150398
Commit-Queue: Haiyang Pan <hypan@google.com>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#761039}

build/android/pylib/local/emulator/avd.py

@@ -265,11 +265,16 @@ class AvdConfig(object):
       instance = _AvdInstance(self._emulator_path, self._emulator_home,
                               self._config)
       # Enable debug for snapshot when it is set to True
-      debug_tags = 'snapshot' if snapshot else None
+      debug_tags = 'init,snapshot' if snapshot else None
       instance.Start(
           read_only=False, snapshot_save=snapshot, debug_tags=debug_tags)
+      # Android devices with full-disk encryption are encrypted on first boot,
+      # and then get decrypted to continue the boot process (See details in
+      # https://bit.ly/3agmjcM).
+      # Wait for this step to complete since it can take a while for old OSs
+      # like M, otherwise the avd may have "Encryption Unsuccessful" error.
       device_utils.DeviceUtils(instance.serial).WaitUntilFullyBooted(
-          timeout=180, retries=0)
+          decrypt=True, timeout=180, retries=0)
       instance.Stop()
 
       # The multiinstance lock file seems to interfere with the emulator's