Upgrade emulator to emu-master-dev build 8457838 am: 7c0db0a484

Original change: https://android-review.googlesource.com/c/platform/prebuilts/android-emulator/+/2065607

Change-Id: I0a69197c822e4c6fce69adeec37f4b9ab1deef6f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>