<webview>: Allocate the view instance ID from the WebView shim

chrome/browser/guestview/guestview_constants.cc

 // Copyright 2013 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 "chrome/browser/guestview/guestview_constants.h"
 
 namespace guestview {
 
 // Parameters/properties on events.
 const char kIsTopLevel[] = "isTopLevel";
 const char kReason[] = "reason";
 const char kUrl[] = "url";
 
-// Attributes.
-const char kAttributeApi[] = "api";
+// Initialization parameters.
+const char kParameterApi[] = "api";
+const char kParameterInstanceId[] = "instanceId";
 
 // Other.
 const int kInstanceIDNone = 0;
 
 }  // namespace guestview