scale color accuracy check

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When upsampling there is a report that brightness and/or color changes.
To test the accuracy
1. write a unittest that implements a reference scaler
2. do a histogram of color errors and aim for low/zero error versus the 
reference.

Test solid colors with different scale factors and filters
Consider sharing color_test histogram function

Original issue reported on code.google.com by fbarch...@chromium.org on 10 Feb 2015 at 6:25