Mutable symbolizer properties for style functions

This change adds setters for symbolizer properties. In addition, it
introduces a mutable flag on all styles. By default, this is set to
true. ol.style.createStyleFunction sets it to false for all static
styles.

The new setters assert that the mutable flag is true, so whenever an
application tries to set a symbolizer property on a style that was
assigned to a vector layer or feature overlay, the assertion will fail.

src/ol/style/imagestyle.js

@@ -1,6 +1,8 @@
 goog.provide('ol.style.Image');
 goog.provide('ol.style.ImageState');
 
+goog.require('goog.asserts');
+
 
 /**
  * @enum {number}
@@ -63,6 +65,12 @@ ol.style.Image = function(options) {
    */
   this.snapToPixel_ = options.snapToPixel;
 
+  /**
+   * @private
+   * @type {boolean}
+   */
+  this.mutable_ = true;
+
 };
 
 
@@ -150,6 +158,61 @@ ol.style.Image.prototype.getOrigin = goog.abstractMethod;
 ol.style.Image.prototype.getSize = goog.abstractMethod;
 
 
+/**
+ * @param {number} opacity Opacity.
+ */
+ol.style.Image.prototype.setOpacity = function(opacity) {
+  goog.asserts.assert(this.mutable_);
+  this.opacity_ = opacity;
+};
+
+
+/**
+ * @param {boolean} rotateWithView Rotate with map.
+ */
+ol.style.Image.prototype.setRotateWithView = function(rotateWithView) {
+  goog.asserts.assert(this.mutable_);
+  this.rotateWithView_ = rotateWithView;
+};
+
+
+/**
+ * @param {number} rotation Rotation.
+ * @api
+ */
+ol.style.Image.prototype.setRotation = function(rotation) {
+  goog.asserts.assert(this.mutable_);
+  this.rotation_ = rotation;
+};
+
+
+/**
+ * @param {number} scale Scale.
+ * @api
+ */
+ol.style.Image.prototype.setScale = function(scale) {
+  goog.asserts.assert(this.mutable_);
+  this.scale_ = scale;
+};
+
+
+/**
+ * @param {boolean} snapToPixel Snap to pixel?
+ */
+ol.style.Image.prototype.setSnapToPixel = function(snapToPixel) {
+  goog.asserts.assert(this.mutable_);
+  this.snapToPixel_ = snapToPixel;
+};
+
+
+/**
+ * @param {boolean} mutable Mutable.
+ */
+ol.style.Image.prototype.setMutable = function(mutable) {
+  this.mutable_ = mutable;
+};
+
+
 /**
  * @param {function(this: T, goog.events.Event)} listener Listener function.
  * @param {T} thisArg Value to use as `this` when executing `listener`.