Don't set global.performance to undefined if it was initialized already
Don't set global.performance to undefined if it was initialized already

Reviewed By: gaearon

Differential Revision: D6448731

fbshipit-source-id: 8c8c6ff393e452c863f54c83c2e4394fd535dfc5

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