Fix inheritance on rendered connection.

Closure compiler on maximum compression breaks badly due to lack of
@extends attribute.

core/connection.js

@@ -516,8 +516,6 @@ Blockly.Connection.prototype.disconnectInternal_ = function(parentBlock,
 
 /**
  * Respawn the shadow block if there was one connected to the this connection.
- * @return {Blockly.Block} The newly spawned shadow block, or null if none was
- *    spawned.
  * @private
  */
 Blockly.Connection.prototype.respawnShadow_ = function() {
@@ -533,9 +531,7 @@ Blockly.Connection.prototype.respawnShadow_ = function() {
     } else {
       throw 'Child block does not have output or previous statement.';
     }
-    return blockShadow;
   }
-  return null;
 };
 
 /**

core/rendered_connection.js

@@ -33,6 +33,7 @@ goog.require('Blockly.Connection');
  * Class for a connection between blocks that may be rendered on screen.
  * @param {!Blockly.Block} source The block establishing this connection.
  * @param {number} type The type of the connection.
+ * @extends {Blockly.Connection}
  * @constructor
  */
 Blockly.RenderedConnection = function(source, type) {
@@ -334,8 +335,8 @@ Blockly.RenderedConnection.prototype.respawnShadow_ = function() {
   // Respawn the shadow block if there is one.
   var shadow = this.getShadowDom();
   if (parentBlock.workspace && shadow && Blockly.Events.recordUndo) {
-    var blockShadow =
-        Blockly.RenderedConnection.superClass_.respawnShadow_.call(this);
+    Blockly.RenderedConnection.superClass_.respawnShadow_.call(this);
+    var blockShadow = this.targetBlock();
     if (!blockShadow) {
       throw 'Couldn\'t respawn the shadow block that should exist here.';
     }