Simple demo for showing how to use an MBTiles file as a data source with Tangram ES in Android. The most salient issues I found were that the MBTiles must be in the app's internal or external file system storage, not in assets, because SQLite can't read a file directly from assets.
Here's how I prepped the MBTiles file from thematicmapping.org's World Borders Dataset with tl, since that wasn't immediately obvious to me either. This assumes you have node and npm installed.
# Install tilelive stuff
npm install -g tl @mapbox/tilelive-omnivore @mapbox/mbtiles
# Get the data
wget http://thematicmapping.org/downloads/TM_WORLD_BORDERS_SIMPL-0.3.zip
unzip TM_WORLD_BORDERS_SIMPL-0.3.zip
# Create the MBTiles file in the app's assets directory
tl copy -z 0 -Z 5 omnivore:///absolute/path/to/TM_WORLD_BORDERS_SIMPL-0.3.shp mbtiles:///absolute/path/to/TangramAndroidMBTilesDemo/app/src/main/assets/tm_world_borders.mbtiles