WebView: update docs for WebView#initSafeBrowsing

This fixes the documentation to specify that an application Context will
be used instead of an Activity Context (since only application Context
is needed).

Bug: 62192626, 63616213
Test: N/A
Change-Id: Ia34d2172be8cca7cb0751286c6c2388ff34d3f4a
1 file changed