set -e on assemble_apk.sh (flutter#17588)

* set -e on assemble_apk.sh

* build the necessary artifacts

Author: dnfield

testing/scenario_app/assemble_apk.sh

@@ -1,5 +1,12 @@
 #!/bin/bash
 
+set -e
+
+pushd "${BASH_SOURCE%/*}/../../.."
+  ./flutter/tools/gn --unopt
+  ninja -C out/host_debug_unopt sky_engine sky_services
+popd
+
 pushd "${BASH_SOURCE%/*}"
   ./compile_android_aot.sh "$1" "$2"
 popd