[android] Add a method to make map snapshots

Fixes: https://github.com/mapbox/mapbox-gl-native/issues/3466

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

@@ -23,6 +23,7 @@ import android.location.Location;
 import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
 import android.net.Uri;
+import android.os.AsyncTask;
 import android.os.Bundle;
 import android.support.annotation.CallSuper;
 import android.support.annotation.FloatRange;
@@ -2453,6 +2454,28 @@ public class MapView extends FrameLayout {
         mMapboxMap = mapboxMap;
     }
 
+    @UiThread
+    void snapshot(@NonNull final MapboxMap.SnapshotReadyCallback callback, @Nullable final Bitmap bitmap) {
+        final TextureView textureView = (TextureView) findViewById(R.id.textureView);
+        final boolean canUseBitmap = bitmap != null && textureView.getWidth() == bitmap.getWidth() && textureView.getHeight() == bitmap.getHeight();
+
+        new AsyncTask<Void, Void, Bitmap>() {
+            @Override
+            protected Bitmap doInBackground(Void... params) {
+                if (canUseBitmap) {
+                    return textureView.getBitmap(bitmap);
+                } else {
+                    return textureView.getBitmap();
+                }
+            }
+
+            @Override
+            protected void onPostExecute(Bitmap bitmap) {
+                callback.onSnapshotReady(bitmap);
+            }
+        }.execute();
+    }
+
     //
     // View utility methods
     //

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

@@ -1,5 +1,6 @@
 package com.mapbox.mapboxsdk.maps;
 
+import android.graphics.Bitmap;
 import android.location.Location;
 import android.os.SystemClock;
 import android.support.annotation.FloatRange;
@@ -1468,6 +1469,16 @@ public class MapboxMap {
         mMapView.update();
     }
 
+    @UiThread
+    public void snapshot(@NonNull SnapshotReadyCallback callback, @Nullable final Bitmap bitmap) {
+        mMapView.snapshot(callback, bitmap);
+    }
+
+    @UiThread
+    public void snapshot(@NonNull SnapshotReadyCallback callback) {
+        mMapView.snapshot(callback, null);
+    }
+
     //
     // Interfaces
     //
@@ -1689,6 +1700,10 @@ public class MapboxMap {
         void onFinish();
     }
 
+    public interface SnapshotReadyCallback {
+        void onSnapshotReady(Bitmap snapshot);
+    }
+
     private class MapChangeCameraPositionListener implements MapView.OnMapChangedListener {
 
         private static final long UPDATE_RATE_MS = 400;