android: make avd screens 960x480.

results in a screen width of 480dp, which should put it in the
middle of large portrait phones per https://bit.ly/311hcJ1

Bug: 922145
Change-Id: I7bb00196dfa48a53467dc35646b81160f9fd8892
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1849429
Commit-Queue: John Budorick <jbudorick@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Auto-Submit: John Budorick <jbudorick@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704446}

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

@@ -231,6 +231,9 @@ class AvdConfig(object):
         config_ini_file.write(
             textwrap.dedent("""\
                 disk.dataPartition.size=4G
+                hw.lcd.density=160
+                hw.lcd.height=960
+                hw.lcd.width=480
                 """))
 
       # Start & stop the AVD.