runtime/race: add tests for maps with big keys/vals With the recent GC changes large objects are handled somewhat differently.
runtime/race: add tests for maps with big keys/vals
With the recent GC changes large objects are handled somewhat differently.

LGTM=khr
R=khr
CC=golang-codereviews
https://codereview.appspot.com/114600043

d0f/go-zh,bryanxu/go-zh,bryanxu/go-zh,webfd/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,d0f/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,d0f/go-zh,webfd/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,d0f/go-zh