TestScaleSamples_Opt can be slow on ARM if the size of the buffer is 1 MB.
This test does a memcpy and behaves the same.

Bug: libyuv:738
Test: LibYUVPlanarTest.TestCopySamples_Opt
Change-Id: Ia9f30190ed76ea350ebe054c9b899d5268e7e135
Reviewed-on: https://chromium-review.googlesource.com/685751Reviewed-by: Cheng Wang <wangcheng@google.com>
Commit-Queue: Frank Barchard <fbarchard@google.com>