Add Viewer.getOverlayById and Overlay.getBounds functions

src/overlay.js

@@ -312,6 +312,14 @@
             this.placement  = location instanceof $.Point ?
                 placement :
                 $.OverlayPlacement.TOP_LEFT;
+        },
+        /**
+         * @function
+         * @returns {OpenSeadragon.Rect} overlay bounds
+         */
+        getBounds: function() {
+
+            return this.bounds;
         }
 
     };

src/viewer.js

@@ -1944,7 +1944,28 @@ $.extend( $.Viewer.prototype, $.EventSource.prototype, $.ControlDock.prototype,
         this.raiseEvent( 'clear-overlay', {} );
         return this;
     },
+    
+     /**
+     * Finds an overlay identified by the reference element or element id
+     * and returns it as an object, return false if not found.
+     * @method
+     * @param {Element|String} element - A reference to the element or an
+     *      element id which represent the ovelay content to be removed.
+     * @return {OpenSeadragon.Overlay} Chainable.
+     */
+    getOverlayById: function( element ) {
+        var i;
 
+        element = $.getElement( element );
+        i = getOverlayIndex( this.currentOverlays, element );    
+        
+        if (i>=0) {
+            return this.currentOverlays[i];
+        } else {
+            return false;
+        }
+        
+    },
     /**
      * Updates the sequence buttons.
      * @function OpenSeadragon.Viewer.prototype._updateSequenceButtons