Upgrade emulator to emu-master-dev build 6940967 am: c3d6cbef6e am: 6ab3c7a610 am: 2d32c4a135

Original change: https://android-review.googlesource.com/c/platform/prebuilts/android-emulator/+/1480981

Change-Id: I5ac598b6d0b85473b90deb6bf293950d46931677