If failUrl(now historyUrl) is null, use "about:blank" instead of "".

This prevents a crash that is caused by calling
WebView.loadDataWithBaseUrl with a null failUrl (which I have renamed
to historyUrl).  Also update the docs to be more accurate.

Fixes the general case of bug 2522457

Change-Id: I832351ce1e0016b00e924a2f9b0097ae15fba34a
4 files changed