JSBigString to MAP_PRIVATE not MAP_SHARED
JSBigString to MAP_PRIVATE not MAP_SHARED

Reviewed By: mhorowitz

Differential Revision: D6613463

fbshipit-source-id: 2553a0475ade061f3b70ffce90fcf4e0ceb7d9fa

ptmt/react-native-macos,facebook/react-native,hoastoolshop/react-native,exponentjs/react-native,rickbeerendonk/react-native,arthuralee/react-native,pandiaraj44/react-native,hoastoolshop/react-native,jevakallio/react-native,javache/react-native,ptmt/react-native-macos,janicduplessis/react-native,hoastoolshop/react-native,ptmt/react-native-macos,dikaiosune/react-native,hammerandchisel/react-native,dikaiosune/react-native,facebook/react-native,exponent/react-native,hammerandchisel/react-native,pandiaraj44/react-native,hoangpham95/react-native,myntra/react-native,jevakallio/react-native,jevakallio/react-native,rickbeerendonk/react-native,myntra/react-native,hammerandchisel/react-native,ptmt/react-native-macos,hoastoolshop/react-native,pandiaraj44/react-native,myntra/react-native,exponent/react-native,facebook/react-native,javache/react-native,janicduplessis/react-native,jevakallio/react-native,rickbeerendonk/react-native,exponentjs/react-native,exponentjs/react-native,javache/react-native,exponent/react-native,janicduplessis/react-native,exponentjs/react-native,dikaiosune/react-native,exponent/react-native,ptmt/react-native-macos,exponentjs/react-native,facebook/react-native,exponentjs/react-native,pandiaraj44/react-native,dikaiosune/react-native,myntra/react-native,hammerandchisel/react-native,myntra/react-native,facebook/react-native,hammerandchisel/react-native,dikaiosune/react-native,pandiaraj44/react-native,myntra/react-native,hoangpham95/react-native,hoastoolshop/react-native,ptmt/react-native-macos,pandiaraj44/react-native,hoangpham95/react-native,facebook/react-native,hoastoolshop/react-native,exponent/react-native,exponent/react-native,janicduplessis/react-native,jevakallio/react-native,arthuralee/react-native,hoastoolshop/react-native,exponentjs/react-native,ptmt/react-native-macos,janicduplessis/react-native,dikaiosune/react-native,facebook/react-native,pandiaraj44/react-native,myntra/react-native,janicduplessis/react-native,rickbeerendonk/react-native,rickbeerendonk/react-native,janicduplessis/react-native,hammerandchisel/react-native,arthuralee/react-native,exponentjs/react-native,javache/react-native,rickbeerendonk/react-native,rickbeerendonk/react-native,dikaiosune/react-native,jevakallio/react-native,javache/react-native,pandiaraj44/react-native,jevakallio/react-native,javache/react-native,facebook/react-native,arthuralee/react-native,rickbeerendonk/react-native,hammerandchisel/react-native,ptmt/react-native-macos,hoangpham95/react-native,exponent/react-native,hoastoolshop/react-native,myntra/react-native,dikaiosune/react-native,hoangpham95/react-native,javache/react-native,arthuralee/react-native,facebook/react-native,hoangpham95/react-native,hoangpham95/react-native,hoangpham95/react-native,jevakallio/react-native,jevakallio/react-native,exponent/react-native,rickbeerendonk/react-native,hammerandchisel/react-native,javache/react-native,javache/react-native,myntra/react-native,janicduplessis/react-native