When run with --enable-ec_adapt, forward updates to the tx_size_prob
 array will not be made.

objective-1-fast:

master-ec_adapt-e568e6f0@2017-02-17T15:30:27.109Z ->
 tx_size-ec_adapt@2017-02-17T15:31:49.504Z

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.0113 | -0.0112 | -0.0113 |  -0.0114 | -0.0114 | -0.0114 |    -0.0112

master-ec_adapt-robust-e568e6f0@2017-02-17T20:29:45.315Z ->
 tx_size-ec_adapt-robust@2017-02-17T20:33:06.405Z

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.0244 | -0.0243 | -0.0243 |  -0.0245 | -0.0245 | -0.0245 |    -0.0243

Change-Id: I5873c5d14e3f3868997775f85fa743d2d55d81b7