[turbofan] Implement simplistic checkpoint reducer.

src/compiler/checkpoint-elimination.h

+// Copyright 2016 the V8 project 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 V8_COMPILER_CHECKPOINT_ELIMINATION_H_
+#define V8_COMPILER_CHECKPOINT_ELIMINATION_H_
+
+#include "src/compiler/graph-reducer.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+// Performs elimination of redundant checkpoints within the graph.
+class CheckpointElimination final : public AdvancedReducer {
+ public:
+  explicit CheckpointElimination(Editor* editor);
+  ~CheckpointElimination() final {}
+
+  Reduction Reduce(Node* node) final;
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_CHECKPOINT_ELIMINATION_H_