Replace further questionable HashMap::add usages in bindings

BUG=390928
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/411273002

git-svn-id: svn://svn.chromium.org/blink/trunk@178823 bbb929c8-8fbe-4397-9dbb-9b2b20218538
    bool readString(v8::Handle<v8::Value>* value)
    {
        uint32_t length;
        if (!doReadUint32(&length))
            return false;
        if (m_position + length > m_length)
            return false;
        *value = v8::String::NewFromUtf8(isolate(), reinterpret_cast<const char*>(m_buffer + m_position), v8::String::kNormalString, length);
        m_position += length;
        return true;
    }

    bool readString(v8::Handle<v8::Value>* value)
    {
        uint32_t length;
        if (!doReadUint32(&length))
            return false;
        if (m_position + length > m_length)
            return false;
        *value = v8::String::NewFromUtf8(isolate(), reinterpret_cast<const char*>(m_buffer + m_position), v8::String::kNormalString, length);
        m_position += length;
        return true;
    }
