Fix for skia issue with buffer passed in S32_D565_Blend_Dither_neon.

S32_D565_Blend_Dither_neon works in
chunks and overruns the buffer boundary. Allocating additional 8
bytes to buffer that is passed to the method overcomes this issue.
The buffer allocation is done at the creation of AndroidPixelRef.

CRs-fixed: 568801

Change-Id: I47a643fad9f5a8d1b8a2f3eba9f7f3a99c1ea2a7