Use ol.Disposable instead of goog.Disposable

src/ol/disposable.js

@@ -0,0 +1,30 @@
+goog.provide('ol.Disposable');
+
+/**
+ * Objects that need to clean up after themselves.
+ * @constructor
+ */
+ol.Disposable = function() {};
+
+/**
+ * The object has already been disposed.
+ * @type {boolean}
+ * @private
+ */
+ol.Disposable.prototype.disposed_ = false;
+
+/**
+ * Clean up.
+ */
+ol.Disposable.prototype.dispose = function() {
+  if (!this.disposed_) {
+    this.disposed_ = true;
+    this.disposeInternal();
+  }
+};
+
+/**
+ * Extension point for disposable objects.
+ * @protected
+ */
+ol.Disposable.prototype.disposeInternal = function() {};