Allow extension APIs to be called from WebUI.

extensions/renderer/resources/binding.js

 // Copyright 2014 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.
 
 var Event = require('event_bindings').Event;
 var forEach = require('utils').forEach;
 var GetAvailability = requireNative('v8_context').GetAvailability;
 var logActivity = requireNative('activityLogger');
 var logging = requireNative('logging');
 var process = requireNative('process');
@@ skipping 401 matching lines @@
             throw new Error('NOT IMPLEMENTED (extension_api.json error): ' +
                 'Cannot parse values for type "' + type + '"');
           }
           m[propertyName] = value;
         }
       });
     };
 
     addProperties(mod, schema);
 
-    var availability = GetAvailability(schema.namespace);
-    if (!availability.is_available && $Object.keys(mod).length == 0) {
+    // This generate() call is considered successful if any functions,
+    // properties, or events were created.
+    var success = ($Object.keys(mod).length > 0);
+
+    // The special case is runtime.lastError which is only occasionally set, so
+    // specifically check its availability.
+    if (schema.namespace == 'runtime' &&
+        GetAvailability('runtime.lastError').is_available) {
+      success = true;
+    }
+
+    if (!success) {
+      // If an API was available it should have been successfully generated.
+      logging.DCHECK(!GetAvailability(schema.namespace).is_available);
       console.error('chrome.' + schema.namespace + ' is not available: ' +
-                        availability.message);
+                    availability.message);
       return;
     }
 
     this.runHooks_(mod);
     return mod;
   }
 };
 
 exports.Binding = Binding;