ConvertToI420 and ConvertToARGB support the use of a negative height
parameter to flip the image vertically. When converting from NV12 or
NV21 this parameter was misinterpreted, resulting in invalid output.
This CL introduces the use of abs_src_height to correctly calculate
the location of the source UV plane.

The sign of crop_height is not used, to reduce confusion ConvertToI420
and ConvertToARGB no longer accept negative crop height.

Unit tests for Android420ToI420 are updated to fix miscalculation of
src_stride_uv, fix incorrect pixel strides, and to test inversion.
New unit tests are included to test inversion for ConvertToARGB,
ConvertToI420, Android420ToARGB, and Android420ToABGR.
For consistency the test NV12Crop is renamed ConvertToI420_NV12_Crop.

Bug: libyuv:446
Test: out/Release/libyuv_unittest --gtest_filter=*.ConvertTo*:*.Android420To*
Change-Id: Idc98e62671cb30272cfa7e24fafbc8b73712f7c6
Reviewed-on: https://chromium-review.googlesource.com/994074
Commit-Queue: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: Frank Barchard <fbarchard@chromium.org>