Create test app that mimics GMail

This CL creates a test app that emulates GMail's list view
for implementing ironwood P0 CUJs (b/244261364).
Demo: https://screenshot.googleplex.com/B8fup8QChvJHMWz.png

Test: manual
Bug: 244261364
Bug: 242247304
Bug: 232584723
Change-Id: Ic7259007c1e6fc3991fc799a62816749b0b64c62
Merged-In: Ic7259007c1e6fc3991fc799a62816749b0b64c62