I420Rotate + kRotate180 doesn't work. about libyuv HOT 4 CLOSED

Note on this line: src_uplane + (width * height / 4);
it wont be quite right for odd width/height.
best to compute
int half_width = (width + 1) / 2;
int half_height = (height + 1) / 2;
unsigned char * src_vplane = src_uplane + half_width * half_height;

The main issue is you're passing src as destination.  Unfortunately I didn't 
anticipate that one and it won't work in the current code.

The way the function works internally is it writes each row of destination, 
starting at the top left, with a horizontally mirrored row, starting the reads 
at the last row.
It would be difficult to make 90 and 270 degree rotation work, but it would be 
possible to make 180 work, if it swapped 2 rows at a time.

r227 adds I420Rotate by 180 in place

1. ConvertToI420 now has the ability to rotate anything (ie MJPG) using a 
temporary buffer.  So it was easy to add a check for destination==source and 
use the buffer to allow rotate to work 'in-place'.  But it wont really be 
inplace.

2. I420Rotate does 2 rows at a time, swapping them and mirroring.
Performance is only marginally slower, but more flexible, so I always use the 
new approach for better code coverage.

Before:
ConstructI420Rotate0 (455 ms)
ConstructI420Rotate90 (921 ms)
ConstructI420Rotate180 (425 ms)
ConstructI420Rotate270 (922 ms)

After
ConstructI420Rotate0 (460 ms)
ConstructI420Rotate90 (917 ms)
ConstructI420Rotate180 (461 ms)
ConstructI420Rotate270 (911 ms)

r247 fixes a Neon rotate issue.