Default initialize RCTNetworking with observation disabled
Default initialize RCTNetworking with observation disabled

Summary:
## Context
When you add/remove listeners from event emitters in JavaScript on iOS, we [call the NativeModule's addListener/removeListener methods](https://fburl.com/diffusion/4878jv6p). These addListener() and removeListener() methods [are implemented on the RCTEventEmitter class](https://fburl.com/diffusion/y913pqhy). All event emitters on iOS are subclasses of RCTEventEmitter.

The only purpose of calling RCTEventEmitter's addListener() and removeListener() methods is to call the [subclasses' startObservation, and stopObservation methods](https://fburl.com/diffusion/rpzyfppk), and [increment/decrement a listenerCount member variable](https://fburl.com/diffusion/ktl8if26) in RCTEventEmitter, which helps catch memory leaks.

RCTNetworking is a subclass of RCTEventEmitter, but it doesn't implement these startObserving/stopObserving methods. Since the [listenerCount is only used to show warnings](https://fburl.com/diffusion/i45lobil), in D24272560 (https://github.com/facebook/react-native/commit/82187bfb6b54fdffc5dadaa56e8bf97d2209708a), I disabled observation in RCTNetworking on the native side. Then in D24272663 (https://github.com/facebook/react-native/commit/dabca52f77799bcdedb6b0ec44b1f6297483a46d), I disabled RCTNetworking.addListener/removeListener NativeModule calls in JavaScript. This was gated via a QE/MC.

## Problem
The default initializer of RCTNetworking doesn't initialize with observation disabled. This broke antwerp when we shipped the experiment in D24272663 (https://github.com/facebook/react-native/commit/dabca52f77799bcdedb6b0ec44b1f6297483a46d). This diff fixes that problem.

Changelog: [Internal]

Reviewed By: fkgozali

Differential Revision: D25671343

fbshipit-source-id: d9a8ba5324a23ade8f4b0bf2ec093f3e4fb494dc

javache/react-native,facebook/react-native,facebook/react-native,facebook/react-native,pandiaraj44/react-native,facebook/react-native,janicduplessis/react-native,facebook/react-native,pandiaraj44/react-native,janicduplessis/react-native,javache/react-native,facebook/react-native,pandiaraj44/react-native,janicduplessis/react-native,janicduplessis/react-native,pandiaraj44/react-native,arthuralee/react-native,myntra/react-native,janicduplessis/react-native,javache/react-native,javache/react-native,javache/react-native,arthuralee/react-native,janicduplessis/react-native,myntra/react-native,pandiaraj44/react-native,javache/react-native,facebook/react-native,janicduplessis/react-native,arthuralee/react-native,javache/react-native,janicduplessis/react-native,myntra/react-native,myntra/react-native,pandiaraj44/react-native,myntra/react-native,myntra/react-native,myntra/react-native,pandiaraj44/react-native,myntra/react-native,facebook/react-native,facebook/react-native,myntra/react-native,pandiaraj44/react-native,arthuralee/react-native,javache/react-native,arthuralee/react-native,javache/react-native