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On UI, the text for installing a WebAPK in the App Banner is:
1) "Add to Homescreen" -> "Adding" -> "Open" for a sucessful
   installation
2) "Add to Homescreen" -> "Adding" -> "Unable to save" toast
   for an unsucessful installation.

WebAPK-specific logic is added to AppBannerInfobarDelegateAndroid
to show the above text. Besides, checking whether a site is WebAPK
Compattive is based on 1) installable check + 2) url is over
 "https" + 3) WebAPK is enabled on command line.

Currently, WebAPK is installed as an untrusted source with Android
installation dialog pops up. User could choose cancel the installation
even after the WebAPK has been downloaded locally. To detect the
cancel behavior, AppBannerInfobarDelegateAndroid checks whether the
WebAPK has been installed or not after Chrome is resumed. This isn't an
ideal way, but it seems we can't find a better way to detect the cancel
event. This logic will be removed when WebAPK is installed by Play soon.

This CL disables creating WebAPKs by selecting add-to-homescreen from
the app menu. Instead, in a follow up CL, selecting from the app menu
will make the app banner info bar shown to install WebAPKs.

BUG=627250

Review-Url: https://codereview.chromium.org/2259553002
Cr-Commit-Position: refs/heads/master@{#415365}