Add basic webview test for Instant Apps

This verifies that Instant Apps can properly load the code required to
start up a WebView.

Test: cts-tradefed run commandAndExit cts-dev -m
CtsAppSecurityHostTestCases -t
android.appsecurity.cts.EphemeralTest#testWebViewLoads

Change-Id: I3aa9c4252423a1a9daf539a4f7d9dd7013fa5a76
5 files changed