Fix a couple more compiler warnings

Fixes warnings in some internal builds.

Author: rictic

externs/webcomponents-externs.js

@@ -32,6 +32,7 @@ window.HTMLImports = HTMLImports;
 var ShadyDOM = {};
 
 ShadyDOM.inUse;
+ShadyDOM.composedPath;
 
 ShadyDOM.flush = function() {};
 

lib/utils/boot.js

@@ -13,8 +13,8 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
  * When using Closure Compiler, JSCompiler_renameProperty(property, object) is replaced by the munged name for object[property]
  * We cannot alias this function, so we have to use a small shim that has the same behavior when not compiling.
  *
- * @param {string} prop Property name
- * @param {?Object} obj Reference object
+ * @param {?} prop Property name
+ * @param {*} obj Reference object
  * @return {string} Potentially renamed property name
  */
 window.JSCompiler_renameProperty = function(prop, obj) {