Warn conflicts with Blockly.Generator.prototype (#1603)

Console warning if block prototypeName conflicts with Blockly.Generator.prototype.

core/block.js

@@ -30,6 +30,7 @@ goog.require('Blockly.Blocks');
 goog.require('Blockly.Comment');
 goog.require('Blockly.Connection');
 goog.require('Blockly.Extensions');
+goog.require('Blockly.Generator');
 goog.require('Blockly.Input');
 goog.require('Blockly.Mutator');
 goog.require('Blockly.Warning');
@@ -52,6 +53,14 @@ goog.require('goog.string');
  * @constructor
  */
 Blockly.Block = function(workspace, prototypeName, opt_id) {
+  if (typeof Blockly.Generator.prototype[prototypeName] !== 'undefined') {
+    console.warn('FUTURE ERROR: Block prototypeName "' + prototypeName
+        + '" conflicts with Blockly.Generator members. Registering Generators '
+        + 'for this block type will incur errors.'
+        + '\nThis name will be DISALLOWED (throwing an error) in future '
+        + 'versions of Blockly.');
+  }
+
   /** @type {string} */
   this.id = (opt_id && !workspace.getBlockById(opt_id)) ?
       opt_id : Blockly.utils.genUid();