[layoutng] Add a base class for layout algorithms

third_party/WebKit/Source/core/layout/ng/ng_layout_algorithm.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 NGLayoutAlgorithm_h
+#define NGLayoutAlgorithm_h
+
+#include "core/CoreExport.h"
+#include "wtf/Allocator.h"
+#include "wtf/Noncopyable.h"
+
+namespace blink {
+
+class NGConstraintSpace;
+class NGFragment;
+
+// Base class for all LayoutNG algorithms.
+class CORE_EXPORT NGLayoutAlgorithm {
+  WTF_MAKE_NONCOPYABLE(NGLayoutAlgorithm);
+  USING_FAST_MALLOC(NGLayoutAlgorithm);
+
+ public:
+  NGLayoutAlgorithm() {}
+
+  // Actual layout function. Lays out the children and descendents within the
+  // constraints given by the NGConstraintSpace. Returns a fragment with the
+  // resulting layout information.
+  // This function can not be const because for interruptible layout, we have
+  // to be able to store state information.
+  virtual NGFragment* layout(const NGConstraintSpace&) = 0;
+};
+
+}  // namespace blink
+
+#endif  // NGLayoutAlgorithm_h