always set the initial-scale

Conversation view's design implies that the page-scale is always 1.0,
since zooming out is done on a per-message basis.

Legacy WebView defaulted to this, but Chromium WebView needs it set
explicitly.

Bug: 10372999
Change-Id: I586557e6c3aac56ea95938697f2ad0640dab002b
1 file changed