[Extensions Bindings] Add a GetStringPropertyFromObject test method

extensions/renderer/api_binding_test_util.cc

 // Copyright 2016 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.
 
 #include "extensions/renderer/api_binding_test_util.h"
 
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
 #include "base/strings/string_util.h"
 #include "base/values.h"
@@ skipping 157 matching lines @@
   return result;
 }
 
 std::unique_ptr<base::Value> GetBaseValuePropertyFromObject(
     v8::Local<v8::Object> object,
     v8::Local<v8::Context> context,
     base::StringPiece key) {
   return V8ToBaseValue(GetPropertyFromObject(object, context, key), context);
 }
 
+std::string GetStringPropertyFromObject(v8::Local<v8::Object> object,
+                                        v8::Local<v8::Context> context,
+                                        base::StringPiece key) {
+  v8::Local<v8::Value> v8_val = GetPropertyFromObject(object, context, key);
+  if (v8_val.IsEmpty())
+    return "empty";
+  if (v8_val->IsNull())
+    return "null";
+  if (v8_val->IsUndefined())
+    return "undefined";
+  if (v8_val->IsFunction())
+    return "function";
+  std::unique_ptr<base::Value> json_prop = V8ToBaseValue(v8_val, context);
+  DCHECK(json_prop) << key;
+  return ValueToString(*json_prop);
+}
+
 }  // namespace extensions