[Typed OM] Remove MutableStylePropertyMap - it seems unnecessary.

third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h

Index: third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h
diff --git a/third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h b/third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h
deleted file mode 100644
index ab6e63a76148f833006e4392c57711d3b70ddcc6..0000000000000000000000000000000000000000
--- a/third_party/WebKit/Source/core/css/cssom/MutableStylePropertyMap.h
+++ /dev/null
@@ -1,21 +0,0 @@
-// Copyright 2016 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.
-
-#ifndef MutableStylePropertyMap_h
-#define MutableStylePropertyMap_h
-
-#include "core/css/cssom/StylePropertyMap.h"
-
-namespace blink {
-
-class CORE_EXPORT MutableStylePropertyMap : public StylePropertyMap {
-  WTF_MAKE_NONCOPYABLE(MutableStylePropertyMap);
-
- protected:
-  MutableStylePropertyMap() = default;
-};
-
-}  // namespace blink
-
-#endif