Check and canonicalize CSS selectors before registering PageStateMatchers.

chrome/renderer/resources/extensions/declarative_content_custom_bindings.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Custom binding for the declarativeContent API.
 
 var binding = require('binding').Binding.create('declarativeContent');
 
 var utils = require('utils');
 var validate = require('schemaUtils').validate;
+var canonicalizeCompoundSelector =
+    requireNative('css_natives').CanonicalizeCompoundSelector;
 
 binding.registerCustomHook( function(api) {
   var declarativeContent = api.compiledApi;
 
   // Returns the schema definition of type |typeId| defined in |namespace|.
   function getSchema(typeId) {
     return utils.lookup(api.schema.types,
                         'id',
                         'declarativeContent.' + typeId);
   }
 
   // Helper function for the constructor of concrete datatypes of the
   // declarative content API.
   // Makes sure that |this| contains the union of parameters and
   // {'instanceType': 'declarativeContent.' + typeId} and validates the
   // generated union dictionary against the schema for |typeId|.
   function setupInstance(instance, parameters, typeId) {
     for (var key in parameters) {
       if ($Object.hasOwnProperty(parameters, key)) {
         instance[key] = parameters[key];
       }
     }
     instance.instanceType = 'declarativeContent.' + typeId;
     var schema = getSchema(typeId);
     validate([instance], [schema]);
   }
 
+  function canonicalizeCssSelectors(selectors) {
+    for (var i = 0; i < selectors.length; i++) {
+      var canonicalizedSelector = canonicalizeCompoundSelector(selectors[i]);
+      if (canonicalizedSelector == '') {
+        throw new Error(
+            'Element of \'css\' array must be a ' +
+            'list of valid compound selectors: ' +
+            selectors[i]);
+      }
+      selectors[i] = canonicalizedSelector;
+    }
+  }
+
   // Setup all data types for the declarative content API.
   declarativeContent.PageStateMatcher = function(parameters) {
     setupInstance(this, parameters, 'PageStateMatcher');
+    if ($Object.hasOwnProperty(this, 'css')) {
+      canonicalizeCssSelectors(this.css);
+    }
   };
   declarativeContent.ShowPageAction = function(parameters) {
     setupInstance(this, parameters, 'ShowPageAction');
   };
 });
 
 exports.binding = binding.generate();