fix SliceHeader: len and cap are int, not uint32
fix SliceHeader: len and cap are int, not uint32

R=r,iant
DELTA=2  (0 added, 0 deleted, 2 changed)
OCL=32215
CL=32222

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go