Merge the value of the push subscription id into the endpoint.

Source/modules/push_messaging/PushSubscription.cpp

Index: Source/modules/push_messaging/PushSubscription.cpp
diff --git a/Source/modules/push_messaging/PushSubscription.cpp b/Source/modules/push_messaging/PushSubscription.cpp
index e7f8779035c5d113d8a08ec774dba76093ea92e6..ef09a4bf2b9df005a0b5efb4cb37dbff318dc7d6 100644
--- a/Source/modules/push_messaging/PushSubscription.cpp
+++ b/Source/modules/push_messaging/PushSubscription.cpp
@@ -40,6 +40,13 @@ PushSubscription::~PushSubscription()
 {
 }
 
+String PushSubscription::endpoint() const
+{
+    // TODO(peter): Remove all plumbing which separates the endpoint from the subscriptionId
+    // after the deprecation period has finished. https://crbug.com/477401.
+    return m_endpoint + "/" + m_subscriptionId;
+}
+
 ScriptPromise PushSubscription::unsubscribe(ScriptState* scriptState)
 {
     RefPtrWillBeRawPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(scriptState);
@@ -55,8 +62,8 @@ ScriptPromise PushSubscription::unsubscribe(ScriptState* scriptState)
 ScriptValue PushSubscription::toJSONForBinding(ScriptState* scriptState)
 {
     V8ObjectBuilder result(scriptState);
-    result.addString("endpoint", m_endpoint);
-    result.addString("subscriptionId", m_subscriptionId);
+    result.addString("endpoint", endpoint());
+    result.addString("subscriptionId", subscriptionId());
 
     return result.scriptValue();
 }