In vp8, statistics are collected about the different modes as they are searched.
This process is more complicated due to the variable block size. Fields were
added to the PICM_MODE_CONTEXT struct to hold this information for each point in
the search. The information is then taken from the appropriate part of the tree
during denoising.

Change-Id: I89261ab77ad637821287ae157dfdf694702b8e77