Update Gaia API documents for #961f7829ea828cdba4fa49e0d407c50123e45e73
    Merge pull request #14912 from davidflanagan/bug939679

Bug 939679: compute the right camera preview size on HD devices r=dmarcos(cherry picked from commit 4245fb93e747d3e3cc9e50ba6fa2f084c9cb682f)