Add WebViewClient#onSafeBrowsingHit() API

This adds the WebViewClient#onSafeBrowsingHit() API and its default
implementation.

This also adds the relevant constants. This includes
SAFE_BROWSING_THREAT_UNKNOWN, in case we expose new threat types in the
future.

Bug: 62723291
Test: N/A
Change-Id: I0b424a952466b23db4cf296573680a0a6c61b981
4 files changed