YUV scale fix

YUV scale fix

There was a scaling mistake visible in some JPEG images because the ratio between Y, U and V planes were assumed to be the same ratios as the ratio between texture sizes, which was wrong because texture have a minimum size of 16 and are rounded up to the next POT. Since the ratios between Y and UV planes are generally 1, 2 or 4, rounding up to the next POT would generally preserve this ratio, so that this bug was not very visible, apart from very small jpeg images of 8 or less pixels in either width or height.

BUG=457954

Review URL: https://codereview.chromium.org/922273002