Reland "Enable tpl model for speed 0"

Reland "Enable tpl model for speed 0"

This is a reland of 9c2c234a0b8f9c08719ac1fa286988a0a3626fd0

Threaded mismatch has been addressed.

Original change's description:
> Enable tpl model for speed 0
>
> Enable adaptive Lagrangian multiplier for arf in speed 0, AQ mode 0,
> and low bit-depth settings. This improves the peak compression
> performance:
>
>           avg PSNR       overall PSNR       SSIM
> low       -0.462%         -0.535%          -0.358%
> mid       -0.780%         -0.857%          -0.868%
> hd        -0.914%         -1.017%          -0.471%
> 720p      -0.624%         -0.671%          -1.553%
> nflx2k    -0.764%         -0.784%          -0.908%
>
> The encoding time at speed 0 is slightly changed to be faster or
> slower:
>
> city_cif 1000 kbps
> 78.2 seconds -> 78.1 seconds
>
> bus_cif 1000 kbps
> 98.6 seconds -> 98.8 seconds.
>
> Change-Id: I18e7337bb61d985cbd3cf29e56439a6cdf675389

BUG=webm:1547

Change-Id: I025a21683ceed23d5f7147e200555b58b791315c