[android] - add line-gradient example, integrate lineProgress expression

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/expressions/Expression.java

@@ -1461,6 +1461,32 @@ public class Expression {
     return new Expression("heatmap-density");
   }
 
+  /**
+   * Gets the progress along a gradient line. Can only be used in the line-gradient property.
+   * <p>
+   * Example usage:
+   * </p>
+   * <pre>
+   * {@code
+   * LineLayer layer = new LineLayer("layer-id", "source-id");
+   * layer.setProperties(
+   *     lineGradient(interpolate(
+   *         linear(), lineProgress(),
+   *         stop(0f, rgb(0, 0, 255)),
+   *         stop(0.5f, rgb(0, 255, 0)),
+   *         stop(1f, rgb(255, 0, 0)))
+   *     )
+   * )
+   * }
+   * </pre>
+   *
+   * @return expression
+   * @see <a href="https://www.mapbox.com/mapbox-gl-js/style-spec/#expressions-line-progress">Style specification</a>
+   */
+  public static Expression lineProgress() {
+    return new Expression("line-progress");
+  }
+
   /**
    * Retrieves an item from an array.
    *

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/sources/GeoJsonOptions.java

@@ -44,6 +44,17 @@ public class GeoJsonOptions extends HashMap<String, Object> {
     return this;
   }
 
+  /**
+   * Initialises whether to calculate line distance metrics.
+   *
+   * @param lineMetrics true to calculate line distance metrics.
+   * @return the current instance for chaining
+   */
+  public GeoJsonOptions withLineMetrics(boolean lineMetrics) {
+    this.put("lineMetrics", lineMetrics);
+    return this;
+  }
+
   /**
    * Douglas-Peucker simplification tolerance (higher means simpler geometries and faster performance).
    *
@@ -88,5 +99,4 @@ public class GeoJsonOptions extends HashMap<String, Object> {
     this.put("clusterRadius", clusterRadius);
     return this;
   }
-
 }