[Web Install] Test cases to include in sample

[amandabaker]

Code: https://github.com/amandabaker/pwa/tree/master/web-install
Site: https://amandabaker.github.io/pwa/web-install/

Same-domain installation:

• Install using preset manifest_id, install_url, and no params
• Install using custom inputs for manifest_id and install_url, no params
• Install using custom inputs
• Install from IFrame (should fail)
• Display and log return value from installation request

Cross-domain scenarios from installer (app store) perspective:

• Install using preset manifest_id, install_url, and no params
• Install using custom inputs for manifest_id and install_url, no params
• Install using custom inputs
• Install from IFrame (should fail)
• Easy options to test installing apps of each install_source flavor
• Log value of GetInstalledApps()

Cross-domain scenarios from installee (to-be-installed app) perspective:

• Have apps that use each variation of install_sources