Add the "silent" property to the NotificationOptions dictionary.

Source/modules/notifications/Notification.h

Index: Source/modules/notifications/Notification.h
diff --git a/Source/modules/notifications/Notification.h b/Source/modules/notifications/Notification.h
index feb01bb8d804d3a5b4b7410ca6816518ea910112..4074afbeba9fe6eeb0739c61ab33505b0d1f502c 100644
--- a/Source/modules/notifications/Notification.h
+++ b/Source/modules/notifications/Notification.h
@@ -82,6 +82,7 @@ public:
     String body() const { return m_body; }
     String tag() const { return m_tag; }
     String icon() const { return m_iconUrl; }
+    bool silent() const { return m_silent; }
 
     TextDirection direction() const;
     KURL iconURL() const { return m_iconUrl; }
@@ -119,6 +120,7 @@ private:
     void setBody(const String& body) { m_body = body; }
     void setIconUrl(KURL iconUrl) { m_iconUrl = iconUrl; }
     void setTag(const String& tag) { m_tag = tag; }
+    void setSilent(bool silent) { m_silent = silent; }
 
     void setPersistentId(const String& persistentId) { m_persistentId = persistentId; }
 
@@ -128,6 +130,7 @@ private:
     String m_lang;
     String m_body;
     String m_tag;
+    bool m_silent;
 
     KURL m_iconUrl;