Use Apple's significant-change API (for iOS 11 UX)

Summary:
In the yet-to-be-released iOS 11, Apple has changed the way they notify the user of location services. (You can watch their session from WWDC about all the changes [here](https://developer.apple.com/videos/play/wwdc2017/713/).)

The current implementation of `RCTLocationObserver` uses the standard location services from Apple. When the user has granted `Always` location permission and the application uses the background location service, the user is presented with the *_Blue Bar of Shame_* (for more information check out [this blog post](https://blog.set.gl/ios-11-location-permissions-and-avoiding-the-blue-bar-of-shame-1cee6cd93bbe)):

![image](https://user-images.githubusercontent.com/15896334/28285133-281e425c-6af9-11e7-9177-61b879ab593c.png)

* Added `useSignificantChanges` boolean to the options passed.

* Added `_usingSignificantChanges` boolean based on user options. If `true`, then the CLLocationManager will use functions `startMonitoringSignificantLocationChanges`/ `stopMonitoringSignificantLocationChanges` rather than the standard location services.
* Changed method signature of `beginLocationUpdatesWithDesiredAccuracy` to include `useSignificantChanges` flag
* Added check for new `NSLocationAlwaysAndWhenInUseUsageDescription`

All unit tests passed.

Tested in simulator and on device, toggling `useSignificantChanges` option when calling `watchPosition`. Results were as expected. **When `TRUE`, the _Blue Bar of Shame_ was not present.**

Changes do not affect Android and location services still work as expected on Android.

* Change is for iOS only
* Using a different API will have different accuracy results. Adding `useSignificantChanges` as an option was by design so apps that want to have most accurate and most frequent update can still use standard location services.
Closes https://github.com/facebook/react-native/pull/15062

Differential Revision: D5443331

Pulled By: javache

fbshipit-source-id: 0cf5b6cd831c5a7c8c25a5ddc2e410a9aa989bf4

Libraries/Geolocation/Geolocation.js

@@ -27,10 +27,11 @@ var subscriptions = [];
 var updatesEnabled = false;
 
 type GeoOptions = {
-  timeout: number,
-  maximumAge: number,
-  enableHighAccuracy: bool,
+  timeout?: number,
+  maximumAge?: number,
+  enableHighAccuracy?: bool,
   distanceFilter: number,
+  useSignificantChanges?: bool,
 }
 
 /**
@@ -124,7 +125,7 @@ var Geolocation = {
 
   /*
    * Invokes the success callback whenever the location changes.  Supported
-   * options: timeout (ms), maximumAge (ms), enableHighAccuracy (bool), distanceFilter(m)
+   * options: timeout (ms), maximumAge (ms), enableHighAccuracy (bool), distanceFilter(m), useSignificantChanges (bool)
    */
   watchPosition: function(success: Function, error?: Function, options?: GeoOptions): number {
     if (!updatesEnabled) {

Libraries/Geolocation/RCTLocationObserver.m

@@ -32,6 +32,7 @@ typedef struct {
   double maximumAge;
   double accuracy;
   double distanceFilter;
+  BOOL useSignificantChanges;
 } RCTLocationOptions;
 
 @implementation RCTConvert (RCTLocationOptions)
@@ -47,7 +48,8 @@ typedef struct {
     .timeout = [RCTConvert NSTimeInterval:options[@"timeout"]] ?: INFINITY,
     .maximumAge = [RCTConvert NSTimeInterval:options[@"maximumAge"]] ?: INFINITY,
     .accuracy = [RCTConvert BOOL:options[@"enableHighAccuracy"]] ? kCLLocationAccuracyBest : RCT_DEFAULT_LOCATION_ACCURACY,
-    .distanceFilter = distanceFilter
+    .distanceFilter = distanceFilter,
+    .useSignificantChanges = [RCTConvert BOOL:options[@"useSignificantChanges"]] ?: NO,
   };
 }
 
@@ -108,6 +110,7 @@ static NSDictionary<NSString *, id> *RCTPositionError(RCTPositionErrorCode code,
   NSDictionary<NSString *, id> *_lastLocationEvent;
   NSMutableArray<RCTLocationRequest *> *_pendingRequests;
   BOOL _observingLocation;
+  BOOL _usingSignificantChanges;
   RCTLocationOptions _observerOptions;
 }
 
@@ -117,7 +120,10 @@ RCT_EXPORT_MODULE()
 
 - (void)dealloc
 {
+  _usingSignificantChanges ?
+    [_locationManager stopMonitoringSignificantLocationChanges] :
     [_locationManager stopUpdatingLocation];
+
   _locationManager.delegate = nil;
 }
 
@@ -133,13 +139,17 @@ RCT_EXPORT_MODULE()
 
 #pragma mark - Private API
 
-- (void)beginLocationUpdatesWithDesiredAccuracy:(CLLocationAccuracy)desiredAccuracy distanceFilter:(CLLocationDistance)distanceFilter
+- (void)beginLocationUpdatesWithDesiredAccuracy:(CLLocationAccuracy)desiredAccuracy distanceFilter:(CLLocationDistance)distanceFilter useSignificantChanges:(BOOL)useSignificantChanges
 {
   [self requestAuthorization];
 
   _locationManager.distanceFilter  = distanceFilter;
   _locationManager.desiredAccuracy = desiredAccuracy;
+  _usingSignificantChanges = useSignificantChanges;
+
   // Start observing location
+  _usingSignificantChanges ?
+    [_locationManager startMonitoringSignificantLocationChanges] :
     [_locationManager startUpdatingLocation];
 }
 
@@ -154,6 +164,8 @@ RCT_EXPORT_MODULE()
 
   // Stop updating if no pending requests
   if (_pendingRequests.count == 0 && !_observingLocation) {
+    _usingSignificantChanges ?
+      [_locationManager stopMonitoringSignificantLocationChanges] :
       [_locationManager stopUpdatingLocation];
   }
 }
@@ -195,7 +207,9 @@ RCT_EXPORT_METHOD(startObserving:(RCTLocationOptions)options)
     _observerOptions.accuracy = MIN(_observerOptions.accuracy, request.options.accuracy);
   }
 
-  [self beginLocationUpdatesWithDesiredAccuracy:_observerOptions.accuracy distanceFilter:_observerOptions.distanceFilter];
+  [self beginLocationUpdatesWithDesiredAccuracy:_observerOptions.accuracy
+                                 distanceFilter:_observerOptions.distanceFilter
+                          useSignificantChanges:_observerOptions.useSignificantChanges];
   _observingLocation = YES;
 }
 
@@ -206,6 +220,8 @@ RCT_EXPORT_METHOD(stopObserving)
 
   // Stop updating if no pending requests
   if (_pendingRequests.count == 0) {
+    _usingSignificantChanges ?
+      [_locationManager stopMonitoringSignificantLocationChanges] :
       [_locationManager stopUpdatingLocation];
   }
 }
@@ -269,7 +285,9 @@ RCT_EXPORT_METHOD(getCurrentPosition:(RCTLocationOptions)options
   if (_locationManager) {
     accuracy = MIN(_locationManager.desiredAccuracy, accuracy);
   }
-  [self beginLocationUpdatesWithDesiredAccuracy:accuracy distanceFilter:options.distanceFilter];
+  [self beginLocationUpdatesWithDesiredAccuracy:accuracy
+                                 distanceFilter:options.distanceFilter
+                          useSignificantChanges:options.useSignificantChanges];
 }
 
 #pragma mark - CLLocationManagerDelegate
@@ -306,6 +324,8 @@ RCT_EXPORT_METHOD(getCurrentPosition:(RCTLocationOptions)options
 
   // Stop updating if not observing
   if (!_observingLocation) {
+    _usingSignificantChanges ?
+      [_locationManager stopMonitoringSignificantLocationChanges] :
       [_locationManager stopUpdatingLocation];
   }
 
@@ -356,8 +376,9 @@ static void checkLocationConfig()
 {
 #if RCT_DEV
   if (!([[NSBundle mainBundle] objectForInfoDictionaryKey:@"NSLocationWhenInUseUsageDescription"] ||
-    [[NSBundle mainBundle] objectForInfoDictionaryKey:@"NSLocationAlwaysUsageDescription"])) {
-    RCTLogError(@"Either NSLocationWhenInUseUsageDescription or NSLocationAlwaysUsageDescription key must be present in Info.plist to use geolocation.");
+    [[NSBundle mainBundle] objectForInfoDictionaryKey:@"NSLocationAlwaysUsageDescription"] ||
+    [[NSBundle mainBundle] objectForInfoDictionaryKey:@"NSLocationAlwaysAndWhenInUseUsageDescription"])) {
+    RCTLogError(@"Either NSLocationWhenInUseUsageDescription or NSLocationAlwaysUsageDescription or NSLocationAlwaysAndWhenInUseUsageDescription key must be present in Info.plist to use geolocation.");
   }
 #endif
 }