android: restore 4G disk.dataPartition.size config for emulator images.

I accidentally removed this in crrev.com/c/1973194, and subsequent
attempts to roll the AVD images have failed on larger test suites as a
result.

Bug: 922145
Change-Id: Ie7b55f456dcd27ec1d17b33814ea258345892c43
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2012790
Commit-Queue: John Budorick <jbudorick@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733903}

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

@@ -241,6 +241,7 @@ class AvdConfig(object):
                  or _DEFAULT_SCREEN_DENSITY)
 
       config_ini_contents = {
+          'disk.dataPartition.size': '4G',
           'hw.lcd.density': density,
           'hw.lcd.height': height,
           'hw.lcd.width': width,