Tuning of factor used to calculate Q range in two pass.
Tuning of factor used to calculate Q range in two pass.

A more detailed explanation of the experimentation
leading to this change can be found in:-

https://docs.google.com/a/google.com/document/d/13lsYhxgPyxUHvEess6wg9nikaonIZKY9Ak_Lpafv5Mo/edit?usp=sharing

This change gives gains across all our standard test sets for
overall psnr, ssim, fast ssim and psnr-HVS.

Values expressed as % reduction in bitrate.

Low res set     -0.257, -0.192, -0.173, -0.101
Mid res set     -0.233, -0.336, -0.367, -0.139
High res set    -0.999, -1.039, -1.111, -0.567
NetFlix 2K set -0.734, -0.174, -0.389, -0.820
Netflix 4K set  -0.814, -0.485, -0.796, -0.839

Change-Id: Ie981fb3c895c9dfcfc8682640d201a86375db5c8

ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx