Give each source file a unique name

src/ol/interaction/dragrotateinteraction.js

@@ -0,0 +1,68 @@
+goog.provide('ol.interaction.DragRotate');
+
+goog.require('ol.MapBrowserEvent');
+goog.require('ol.interaction.ConditionType');
+goog.require('ol.interaction.Drag');
+
+
+
+/**
+ * @constructor
+ * @extends {ol.interaction.Drag}
+ * @param {ol.interaction.ConditionType} condition Condition.
+ */
+ol.interaction.DragRotate = function(condition) {
+
+  goog.base(this);
+
+  /**
+   * @private
+   * @type {ol.interaction.ConditionType}
+   */
+  this.condition_ = condition;
+
+  /**
+   * @private
+   * @type {number}
+   */
+  this.startRotation_ = 0;
+
+};
+goog.inherits(ol.interaction.DragRotate, ol.interaction.Drag);
+
+
+/**
+ * @inheritDoc
+ */
+ol.interaction.DragRotate.prototype.handleDrag = function(mapBrowserEvent) {
+  var browserEvent = mapBrowserEvent.browserEvent;
+  var map = mapBrowserEvent.map;
+  var size = map.getSize();
+  var offset = mapBrowserEvent.getPixel();
+  var theta = Math.atan2(
+      size.height / 2 - offset.y,
+      offset.x - size.width / 2);
+  map.rotate(this.startRotation_, -theta);
+};
+
+
+/**
+ * @inheritDoc
+ */
+ol.interaction.DragRotate.prototype.handleDragStart =
+    function(mapBrowserEvent) {
+  var browserEvent = mapBrowserEvent.browserEvent;
+  var map = mapBrowserEvent.map;
+  if (browserEvent.isMouseActionButton() && this.condition_(browserEvent) &&
+      map.canRotate()) {
+    var size = map.getSize();
+    var offset = mapBrowserEvent.getPixel();
+    var theta = Math.atan2(
+        size.height / 2 - offset.y,
+        offset.x - size.width / 2);
+    this.startRotation_ = (map.getRotation() || 0) + theta;
+    return true;
+  } else {
+    return false;
+  }
+};