V8ObjectBuilder::addString support Nullable.

third_party/WebKit/Source/bindings/core/v8/V8ObjectBuilder.h

 // Copyright 2015 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.
 
 #ifndef V8ObjectBuilder_h
 #define V8ObjectBuilder_h
 
 #include "bindings/core/v8/ToV8.h"
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
@@ skipping 11 matching lines @@
  public:
   explicit V8ObjectBuilder(ScriptState*);
 
   ScriptState* getScriptState() const { return m_scriptState.get(); }
 
   V8ObjectBuilder& add(const String& name, const V8ObjectBuilder&);
 
   V8ObjectBuilder& addNull(const String& name);
   V8ObjectBuilder& addBoolean(const String& name, bool value);
   V8ObjectBuilder& addNumber(const String& name, double value);
-  V8ObjectBuilder& addString(const String& name, const String& value);
+  V8ObjectBuilder& addString(const String& name,

[Yuki, 2016/11/09 07:25:50]

It's okay to follow the old style, but
    const StringView& name,
    const StringView& value,
is now recommended.

+                             const String& value,
+                             bool isNullable = false);

[Yuki, 2016/11/09 07:25:50]

In general, we should avoid a boolean flag, I think.  Given the following code:
    x.addString("key", value, true);
It's not clear what the last argument means.

Blink's coding style recommended enum values instead.
    x.addString("key", value, V8ObjectBuilder::Nullable);

In this specific case, my preference is:
    x.addStringOrNull("key", value);
then, it's short and crystal clear.

 
   template <typename T>
   V8ObjectBuilder& add(const String& name, const T& value) {
     addInternal(name, v8::Local<v8::Value>(
                           toV8(value, m_scriptState->context()->Global(),
                                m_scriptState->isolate())));
     return *this;
   }
 
   ScriptValue scriptValue() const;
   v8::Local<v8::Object> v8Value() const { return m_object; }
 
  private:
   void addInternal(const String& name, v8::Local<v8::Value>);
 
   RefPtr<ScriptState> m_scriptState;
   v8::Local<v8::Object> m_object;
 };
 
 }  // namespace blink
 
 #endif  // V8ObjectBuilder_h