Consolidated logic for pausing/resuming MGLMapboxEvents

`MGLMapboxEvents` automatically recreates its location manager when the host app is reauthorized for Location Services. Added some redundancy to ensure that there is no location manager when either Location Services or Mapbox Metrics is off.

include/mbgl/ios/MGLMapboxEvents.h

@@ -54,4 +54,7 @@ extern NSString *const MGLEventGestureRotateStart;
 //
 + (void) flush;
 
+// Main thread only
++ (void)validate;
+
 @end

platform/ios/MGLMapView.mm

@@ -707,6 +707,8 @@ std::chrono::steady_clock::duration secondsAsDuration(float duration)
     if (self.isDormant)
     {
         self.dormant = NO;
+        
+        [MGLMapboxEvents validate];
 
         self.glSnapshotView.hidden = YES;
 

platform/ios/MGLMapboxEvents.m

@@ -260,12 +260,7 @@ const NSTimeInterval MGLFlushInterval = 60;
                                                                               usingBlock:
          ^(NSNotification *notification) {
              MGLMapboxEvents *strongSelf = weakSelf;
-             BOOL enabledInSettings = [[strongSelf class] isEnabled];
-             if (strongSelf.paused && enabledInSettings) {
-                 [strongSelf resumeMetricsCollection];
-             } else if (!strongSelf.paused && !enabledInSettings) {
-                 [strongSelf pauseMetricsCollection];
-             }
+             [strongSelf validate];
          }];
     }
     return self;
@@ -302,6 +297,38 @@ const NSTimeInterval MGLFlushInterval = 60;
     [self pauseMetricsCollection];
 }
 
++ (void)validate {
+    [[MGLMapboxEvents sharedManager] validate];
+}
+
+- (void)validate {
+    MGLAssertIsMainThread();
+    BOOL enabledInSettings = [[self class] isEnabled];
+    if (self.paused && enabledInSettings) {
+        [self resumeMetricsCollection];
+    } else if (!self.paused && !enabledInSettings) {
+        [self pauseMetricsCollection];
+    }
+    
+    [self validateUpdatingLocation];
+}
+
+- (void)validateUpdatingLocation {
+    MGLAssertIsMainThread();
+    if (self.paused) {
+        [self stopUpdatingLocation];
+    } else {
+        CLAuthorizationStatus authStatus = [CLLocationManager authorizationStatus];
+        if (authStatus == kCLAuthorizationStatusDenied ||
+            authStatus == kCLAuthorizationStatusRestricted) {
+            [self stopUpdatingLocation];
+        } else if (authStatus == kCLAuthorizationStatusAuthorized ||
+                   authStatus == kCLAuthorizationStatusAuthorizedWhenInUse) {
+            [self startUpdatingLocation];
+        }
+    }
+}
+
 + (void)pauseMetricsCollection {
     [[MGLMapboxEvents sharedManager] pauseMetricsCollection];
 }
@@ -321,7 +348,7 @@ const NSTimeInterval MGLFlushInterval = 60;
     [_session invalidateAndCancel];
     _session = nil;
     
-    [self stopUpdatingLocation];
+    [self validateUpdatingLocation];
 }
 
 - (void)stopUpdatingLocation {
@@ -343,17 +370,23 @@ const NSTimeInterval MGLFlushInterval = 60;
 //
 - (void)resumeMetricsCollection {
     MGLAssertIsMainThread();
-    if (!self.isPaused || ![[self class] isEnabled]) {
+    if (!self.paused || ![[self class] isEnabled]) {
         return;
     }
     self.paused = NO;
     _data = [[MGLMapboxEventsData alloc] init];
     _session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:nil];
     
-    [self startUpdatingLocation];
+    [self validateUpdatingLocation];
 }
 
 - (void)startUpdatingLocation {
+    MGLAssertIsMainThread();
+    if (_locationManager || _paused) {
+        NSAssert(!(_locationManager && _paused),
+                 @"MGLMapboxEvents should not have a CLLocationManager while paused.");
+        return;
+    }
     _locationManager = [[CLLocationManager alloc] init];
     _locationManager.desiredAccuracy = kCLLocationAccuracyKilometer;
     _locationManager.distanceFilter = 10;
@@ -742,17 +775,7 @@ const NSTimeInterval MGLFlushInterval = 60;
 }
 
 - (void)locationManager:(CLLocationManager *)manager didChangeAuthorizationStatus:(CLAuthorizationStatus)status {
-    switch (status) {
-        case kCLAuthorizationStatusDenied:
-            [self stopUpdatingLocation];
-            break;
-        case kCLAuthorizationStatusAuthorized:
-        case kCLAuthorizationStatusAuthorizedWhenInUse:
-            [self startUpdatingLocation];
-            break;
-        default:
-            break;
-    }
+    [self validateUpdatingLocation];
 }
 
 #pragma mark NSURLSessionDelegate