Revert of Move SelectionAdjust to its own file

third_party/WebKit/Source/core/editing/SelectionAdjuster.h

-// 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 SelectionAdjuster_h
-#define SelectionAdjuster_h
-
-#include "core/editing/VisibleSelection.h"
-#include "wtf/Allocator.h"
-
-namespace blink {
-
-// |SelectionAdjuster| adjusts positions in |VisibleSelection| directly without
-// calling |validate()|. Users of |SelectionAdjuster| should keep invariant of
-// |VisibleSelection|, e.g. all positions are canonicalized.
-class SelectionAdjuster final {
-    STATIC_ONLY(SelectionAdjuster);
-public:
-    static void adjustSelectionInComposedTree(VisibleSelectionInComposedTree*, const VisibleSelection&);
-    static void adjustSelectionInDOMTree(VisibleSelection*, const VisibleSelectionInComposedTree&);
-    static void adjustSelectionToAvoidCrossingShadowBoundaries(VisibleSelection*);
-    static void adjustSelectionToAvoidCrossingShadowBoundaries(VisibleSelectionInComposedTree*);
-};
-
-} // namespace blink
-
-#endif // SelectionAdjuster_h