[core, darwin, android] Add onDidEnterIdle to MapObserver.

didEnterIdle fires whenever render completes and no repaint is scheduled.

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapChangeReceiver.java

@@ -26,6 +26,8 @@ class MapChangeReceiver implements NativeMapView.StateCallback {
     = new CopyOnWriteArrayList<>();
   private final List<MapView.OnDidFinishRenderingMapListener> onDidFinishRenderingMapListenerList
     = new CopyOnWriteArrayList<>();
+  private final List<MapView.OnDidEnterIdleListener> onDidEnterIdleListenerList
+      = new CopyOnWriteArrayList<>();
   private final List<MapView.OnDidFinishLoadingStyleListener> onDidFinishLoadingStyleListenerList
     = new CopyOnWriteArrayList<>();
   private final List<MapView.OnSourceChangedListener> onSourceChangedListenerList = new CopyOnWriteArrayList<>();
@@ -170,6 +172,20 @@ class MapChangeReceiver implements NativeMapView.StateCallback {
     }
   }
 
+  @Override
+  public void onDidEnterIdle() {
+    try {
+      if (!onDidEnterIdleListenerList.isEmpty()) {
+        for (MapView.OnDidEnterIdleListener listener : onDidEnterIdleListenerList) {
+          listener.onDidEnterIdle();
+        }
+      }
+    } catch (Throwable err) {
+      Logger.e(TAG, "Exception in onDidEnterIdle", err);
+      throw err;
+    }
+  }
+
   @Override
   public void onDidFinishLoadingStyle() {
     try {
@@ -278,6 +294,14 @@ class MapChangeReceiver implements NativeMapView.StateCallback {
     onDidFinishRenderingMapListenerList.remove(listener);
   }
 
+  void addOnDidEnterIdleListener(MapView.OnDidEnterIdleListener listener) {
+    onDidEnterIdleListenerList.add(listener);
+  }
+
+  void removeOnDidEnterIdleListener(MapView.OnDidEnterIdleListener listener) {
+    onDidEnterIdleListenerList.remove(listener);
+  }
+
   void addOnDidFinishLoadingStyleListener(MapView.OnDidFinishLoadingStyleListener listener) {
     onDidFinishLoadingStyleListenerList.add(listener);
   }
@@ -305,6 +329,7 @@ class MapChangeReceiver implements NativeMapView.StateCallback {
     onDidFinishRenderingFrameList.clear();
     onWillStartRenderingMapListenerList.clear();
     onDidFinishRenderingMapListenerList.clear();
+    onDidEnterIdleListenerList.clear();
     onDidFinishLoadingStyleListenerList.clear();
     onSourceChangedListenerList.clear();
   }

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapView.java

@@ -691,12 +691,32 @@ public class MapView extends FrameLayout implements NativeMapView.ViewCallback {
   /**
    * Remove a callback that's invoked when the map has finished rendering.
    *
-   * @param listener The callback that's invoked when the map has finished rendering
+   * @param listener The callback that's invoked when the map has has finished rendering.
    */
   public void removeOnDidFinishRenderingMapListener(OnDidFinishRenderingMapListener listener) {
     mapChangeReceiver.removeOnDidFinishRenderingMapListener(listener);
   }
 
+  /**
+   * Set a callback that's invoked when the map has entered the idle state.
+   *
+   * @param listener The callback that's invoked when the map has entered the idle state.
+   */
+  public void addOnDidEnterIdleListener(OnDidEnterIdleListener listener) {
+    mapChangeReceiver.addOnDidEnterIdleListener(listener);
+  }
+
+  /**
+   * Remove a callback that's invoked when the map has entered the idle state.
+   *
+   * @param listener The callback that's invoked when the map has entered the idle state.
+   */
+  public void removeOnDidEnterIdleListener(OnDidEnterIdleListener listener) {
+    mapChangeReceiver.removeOnDidEnterIdleListener(listener);
+  }
+
+  /**
+
   /**
    * Set a callback that's invoked when the style has finished loading.
    *
@@ -870,6 +890,19 @@ public class MapView extends FrameLayout implements NativeMapView.ViewCallback {
     void onDidFinishRenderingMap(boolean fully);
   }
 
+  /**
+   * Interface definition for a callback to be invoked when the map has entered the idle state.
+   * <p>
+   * {@link MapView#addOnDidEnterIdleListener(OnDidEnterIdleListener)}
+   * </p>
+   */
+  public interface OnDidEnterIdleListener {
+    /**
+     * Called when the map has entered the idle state.
+     */
+    void onDidEnterIdle();
+  }
+
   /**
    * Interface definition for a callback to be invoked when the map has loaded the style.
    * <p>

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/NativeMapView.java

@@ -1009,6 +1009,11 @@ final class NativeMapView {
     }
   }
 
+  @Keep
+  private void onDidEnterIdle() {
+    stateCallback.onDidEnterIdle();
+  }
+
   @Keep
   private void onDidFinishLoadingStyle() {
     if (stateCallback != null) {
@@ -1472,6 +1477,8 @@ final class NativeMapView {
 
     void onDidFinishRenderingMap(boolean fully);
 
+    void onDidEnterIdle();
+
     void onSourceChanged(String sourceId);
   }
 }