Fix memory usage display in Perf Monitor (#19664)
Fix memory usage display in Perf Monitor (#19664)

Summary:
According to: https://github.com/apple/darwin-xnu/blob/master/osfmk/kern/bsd_kern.c#L420
The result is the same as Xcode app memory uesd.

Before Fix:

<img width="250" alt="before" src="https://user-images.githubusercontent.com/22233256/41394508-ce810362-6fdc-11e8-8d40-73703ec93bc3.png">
<img width="266" alt="before1" src="https://user-images.githubusercontent.com/22233256/41394511-d00a9a0e-6fdc-11e8-9f18-2198e8de2410.png">

After Fix:
<img width="270" alt="after" src="https://user-images.githubusercontent.com/22233256/41394517-d5a56ff2-6fdc-11e8-8d19-41e046c4b511.png">
<img width="267" alt="after1" src="https://user-images.githubusercontent.com/22233256/41394520-d7a3c600-6fdc-11e8-98c4-e3024a4532ec.png">

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[IOS] [BUGFIX] [Monitor] - fix memory perf monitor. Make sure the memory footprint is the same as Jetsam.

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Pull Request resolved: https://github.com/facebook/react-native/pull/19664

Differential Revision: D9246307

Pulled By: hramos

fbshipit-source-id: f85efc54cdcb0c19677594d465752c666d5af18b

javache/react-native,janicduplessis/react-native,myntra/react-native,arthuralee/react-native,exponent/react-native,pandiaraj44/react-native,exponent/react-native,arthuralee/react-native,arthuralee/react-native,hoangpham95/react-native,exponentjs/react-native,myntra/react-native,arthuralee/react-native,hammerandchisel/react-native,exponentjs/react-native,janicduplessis/react-native,javache/react-native,hoangpham95/react-native,hoangpham95/react-native,myntra/react-native,janicduplessis/react-native,hammerandchisel/react-native,exponent/react-native,myntra/react-native,exponentjs/react-native,hoangpham95/react-native,pandiaraj44/react-native,myntra/react-native,facebook/react-native,hammerandchisel/react-native,pandiaraj44/react-native,hammerandchisel/react-native,janicduplessis/react-native,javache/react-native,hoangpham95/react-native,exponentjs/react-native,hammerandchisel/react-native,javache/react-native,exponentjs/react-native,janicduplessis/react-native,facebook/react-native,myntra/react-native,javache/react-native,javache/react-native,pandiaraj44/react-native,myntra/react-native,janicduplessis/react-native,exponent/react-native,hammerandchisel/react-native,exponentjs/react-native,janicduplessis/react-native,pandiaraj44/react-native,exponent/react-native,exponent/react-native,facebook/react-native,hoangpham95/react-native,facebook/react-native,hoangpham95/react-native,myntra/react-native,facebook/react-native,janicduplessis/react-native,javache/react-native,exponentjs/react-native,myntra/react-native,hammerandchisel/react-native,facebook/react-native,arthuralee/react-native,facebook/react-native,facebook/react-native,pandiaraj44/react-native,pandiaraj44/react-native,javache/react-native,exponent/react-native,hoangpham95/react-native,pandiaraj44/react-native,exponentjs/react-native,exponent/react-native,facebook/react-native,hammerandchisel/react-native,javache/react-native