Add method stopPropagation and stop to NavigationEvent

Summary: @​public Add method `stopPropagation` and `stop` to NavigationEvent so we can stop event easily once event bubbling and capturing is supported. Reviewed By: @fkgozali Differential Revision: D2471903

Author: Hedger Wang

Libraries/CustomComponents/Navigator/Navigation/NavigationEvent.js

@@ -57,6 +57,7 @@ var _navigationEventPool = new NavigationEventPool();
 class NavigationEvent {
  _data: any;
  _defaultPrevented: boolean;
+ _propagationStopped: boolean;
  _disposed: boolean;
  _target: ?Object;
  _type: ?string;
@@ -71,6 +72,7 @@ class NavigationEvent {
  this._data = data;
  this._defaultPrevented = false;
  this._disposed = false;
+ this._propagationStopped = false;
  }
 
  /* $FlowFixMe - get/set properties not yet supported */
@@ -97,6 +99,19 @@ class NavigationEvent {
  this._defaultPrevented = true;
  }
 
+ stopPropagation(): void {
+ this._propagationStopped = true;
+ }
+
+ stop(): void {
+ this.preventDefault();
+ this.stopPropagation();
+ }
+
+ isPropagationStopped(): boolean {
+ return this._propagationStopped;
+ }
+
  /**
  * Dispose the event.
  * NavigationEvent shall be disposed after being emitted by