[darwin] Simplify MGLStyleLayer initialization and pointer management

Similarly to the previous commit, introduce `-[MGLStyleLayer initWithPendingLayer:]`, allowing the base class to track the owned `_pendingSource` pointer and implement `-addToMapView:` and `-removeFromMapView:` without any casts.

Fixes an issue where `-[MGLStyle layerFromMBGLLayer:]` would wind up creating layers whose `_rawLayer` and `_pendingLayer` held different values.

1 files changed, 15 insertions, 0 deletions

diff --git a/platform/darwin/src/MGLFillStyleLayer.h b/platform/darwin/src/MGLFillStyleLayer.h
index 1f3cfc8af5..89f84185dc 100644
--- a/platform/darwin/src/MGLFillStyleLayer.h
+++ b/platform/darwin/src/MGLFillStyleLayer.h
@@ -52,6 +52,21 @@ typedef NS_ENUM(NSUInteger, MGLFillTranslationAnchor) {
 MGL_EXPORT
 @interface MGLFillStyleLayer : MGLVectorStyleLayer
 
+/**
+ Returns a fill style layer initialized with an identifier and source.
+
+ After initializing and configuring the style layer, add it to a map view’s
+ style using the `-[MGLStyle addLayer:]` or
+ `-[MGLStyle insertLayer:belowLayer:]` method.
+
+ @param identifier A string that uniquely identifies the source in the style to
+    which it is added.
+ @param source The source from which to obtain the data to style. If the source
+    has not yet been added to the current style, the behavior is undefined.
+ @return An initialized foreground style layer.
+ */
+- (instancetype)initWithIdentifier:(NSString *)identifier source:(MGLSource *)source NS_DESIGNATED_INITIALIZER;
+
 #pragma mark - Accessing the Paint Attributes
 
 /**