[android] add unknown layer type

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/UnknownLayer.java

@@ -0,0 +1,25 @@
+package com.mapbox.mapboxsdk.style.layers;
+
+import android.support.annotation.UiThread;
+
+/**
+ * An unknown type of layer
+ */
+@UiThread
+public class UnknownLayer extends Layer {
+
+  /**
+   * Creates a UnknownLayer.
+   *
+   * @param nativePtr pointer used by core
+   */
+  UnknownLayer(long nativePtr) {
+    super(nativePtr);
+  }
+
+  protected native void initialize();
+
+  @Override
+  protected native void finalize() throws Throwable;
+
+}