[Extensions Bindings] Add lastError utilities to APIBindingJSUtil

extensions/renderer/api_bindings_system_unittest.h

Index: extensions/renderer/api_bindings_system_unittest.h
diff --git a/extensions/renderer/api_bindings_system_unittest.h b/extensions/renderer/api_bindings_system_unittest.h
index 2b13f16090c461da177cf17861608980ed413384..614fa47e02b40a1d2af28c969a9f52c157f12316 100644
--- a/extensions/renderer/api_bindings_system_unittest.h
+++ b/extensions/renderer/api_bindings_system_unittest.h
@@ -60,10 +60,11 @@ class APIBindingsSystemTest : public APIBindingTest {
                            const std::string& expected_arguments);
 
   // Wraps the given |script source| in (function(obj) { ... }) and executes
-  // the result function, passing in |object| for an argument.
-  void CallFunctionOnObject(v8::Local<v8::Context> context,
-                            v8::Local<v8::Object> object,
-                            const std::string& script_source);
+  // the result function, passing in |object| for an argument. Returns the
+  // result of calling the function.
+  v8::Local<v8::Value> CallFunctionOnObject(v8::Local<v8::Context> context,
+                                            v8::Local<v8::Object> object,
+                                            const std::string& script_source);
 
   const APIRequestHandler::Request* last_request() const {
     return last_request_.get();