GitLab

This CL:
- Makes WebappActivity use CurrentPageVerifier
- Adds homescreen-shortcut and WebAPK subclasses of Verifier
- Introduces WebappActiveTabUmaTracker for recording metrics about
active tab
- Makes
CustomTabDelegateFactory#shouldDisableExternalIntentRequestsForUrl() use
ExternalIntentsPolicyProvider for Webapps & WebAPKs

BUG=1054718
TESTS=WebApkInitializationTest.testInitialization
      AddToHomescreenCurrentPageVerifierTest.*
      WebApkCurrentPageVerifierTest.*
      CustomTabExternalNavigationTest.testShouldDisableExternalIntentRequestsForUrl

Change-Id: I2bbd0505f28b99569c4bed8fb4e6e10295620eaa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2068116
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Peter Conn <peconn@chromium.org>
Reviewed-by: Glenn Hartmann <hartmanng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751874}