Blink Plugins: Remove Shadow DOM Plugin Placeholder

Source/core/html/shadow/PluginPlaceholderElement.idl

Index: Source/core/html/shadow/PluginPlaceholderElement.idl
diff --git a/Source/core/html/shadow/PluginPlaceholderElement.idl b/Source/core/html/shadow/PluginPlaceholderElement.idl
deleted file mode 100644
index a873f0a669853503f44514e455a53fd9ade8b543..0000000000000000000000000000000000000000
--- a/Source/core/html/shadow/PluginPlaceholderElement.idl
+++ /dev/null
@@ -1,12 +0,0 @@
-// Copyright 2014 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.
-
-[
-    NoInterfaceObject
-] interface PluginPlaceholderElement : HTMLDivElement {
-    [ImplementedInPrivateScript, OnlyExposedToPrivateScript] attribute DOMString message;
-    [ImplementedInPrivateScript, OnlyExposedToPrivateScript] attribute boolean closeable;
-
-    [ImplementedInPrivateScript, OnlyExposedToPrivateScript] void createdCallback();
-};