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 402 matching lines @@
                 'Cannot parse values for type "' + type + '"');
           }
           m[propertyName] = value;
         }
       });
     };
 
     addProperties(mod, schema);
 
     var availability = GetAvailability(schema.namespace);
-    if (!availability.is_available && $Object.keys(mod).length == 0) {
-      console.error('chrome.' + schema.namespace + ' is not available: ' +
-                        availability.message);
-      return;
+    if (!availability.is_available) {
+      // The namespace isn't available, but some of its functions may be, so we
+      // still allow access to the API.
+      //
+      // A special case is runtime.lastError which is only occasionally set, so
+      // specifically check that availability.
+      if ($Object.keys(mod).length == 0 &&
+          !(schema.namespace == 'runtime' &&
+            GetAvailability('runtime.lastError').is_available)) {

[Ken Rockot(use gerrit already), 2014/07/18 22:33:40]

I'm not sure how to make this less confusing, but it took me a few reads to
understand it.

[not at google - send to devlin, 2014/07/18 23:28:35]

I was confused when I re-read my own CL. How does this look?

+        console.error('chrome.' + schema.namespace + ' is not available: ' +
+                      availability.message);
+        return;
+      }
     }
 
     this.runHooks_(mod);
     return mod;
   }
 };
 
 exports.Binding = Binding;