[Extensions Bindings] Add lastError utilities to APIBindingJSUtil

extensions/renderer/api_bindings_system_unittest.cc

Index: extensions/renderer/api_bindings_system_unittest.cc
diff --git a/extensions/renderer/api_bindings_system_unittest.cc b/extensions/renderer/api_bindings_system_unittest.cc
index d9de2d47e3e97acb0599ba4fcee1aff440b204bf..a75274ff341789b7aa098162b626b448095dcd4e 100644
--- a/extensions/renderer/api_bindings_system_unittest.cc
+++ b/extensions/renderer/api_bindings_system_unittest.cc
@@ -172,7 +172,7 @@ void APIBindingsSystemTest::ValidateLastRequest(
             ValueToString(*last_request()->arguments));
 }
 
-void APIBindingsSystemTest::CallFunctionOnObject(
+v8::Local<v8::Value> APIBindingsSystemTest::CallFunctionOnObject(
     v8::Local<v8::Context> context,
     v8::Local<v8::Object> object,
     const std::string& script_source) {
@@ -181,10 +181,14 @@ void APIBindingsSystemTest::CallFunctionOnObject(
 
   v8::Local<v8::Function> func =
       FunctionFromString(context, wrapped_script_source);
-  ASSERT_FALSE(func.IsEmpty());
+  // Use ADD_FAILURE() to avoid messing up the return type with ASSERT.
+  if (func.IsEmpty()) {
+    ADD_FAILURE() << script_source;
+    return v8::Local<v8::Value>();
+  }
 
   v8::Local<v8::Value> argv[] = {object};
-  RunFunction(func, context, 1, argv);
+  return RunFunction(func, context, 1, argv);
 }
 
 // Tests API object initialization, calling a method on the supplied APIs, and