Use prototypes for Connection properties.

core/connection.js

@@ -39,18 +39,47 @@ goog.require('goog.dom');
 Blockly.Connection = function(source, type) {
   /** @type {!Blockly.Block} */
   this.sourceBlock_ = source;
-  /** @type {Blockly.Connection} */
-  this.targetConnection = null;
   /** @type {number} */
   this.type = type;
-  this.x_ = 0;
-  this.y_ = 0;
   // Shortcut for the databases for this connection's workspace.
   this.dbList_ = source.workspace.connectionDBList;
   this.hidden_ = !this.dbList_;
-  this.inDB_ = false;
 };
 
+/**
+ * Connection this connection connects to.  Null if not connected.
+ * @type {Blockly.Connection}
+ */
+Blockly.Connection.prototype.targetConnection = null;
+
+/**
+ * List of compatible value types.  Null if all types are compatible.
+ * @private
+ * @type {Array}
+ */
+Blockly.Connection.prototype.check_ = null;
+
+/**
+ * Horizontal location of this connection.
+ * @private
+ * @type {number}
+ */
+Blockly.Connection.prototype.x_ = 0;
+
+/**
+ * Vertical location of this connection.
+ * @private
+ * @type {number}
+ */
+Blockly.Connection.prototype.y_ = 0;
+
+/**
+ * Has this connection been added to the connection database?
+ * @private
+ * @type {boolean}
+ */
+Blockly.Connection.prototype.inDB_ = false;
+
 /**
  * Sever all links to this connection (not including from the source object).
  */