[turbofan] Proper dead code elimination as regular reducer.

src/compiler/control-reducer.h

-// Copyright 2014 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_CONTROL_REDUCER_H_
-#define V8_COMPILER_CONTROL_REDUCER_H_
-
-namespace v8 {
-namespace internal {
-
-// Forward declarations.
-class Zone;
-
-
-namespace compiler {
-
-// Forward declarations.
-class JSGraph;
-class CommonOperatorBuilder;
-class Node;
-
-class ControlReducer {
- public:
-  // Perform branch folding and dead code elimination on the graph.
-  static void ReduceGraph(Zone* zone, JSGraph* graph,
-                          int max_phis_for_select = 0);
-
-  // Reduces a single merge node and attached phis.
-  static Node* ReduceMerge(JSGraph* graph, Node* node,
-                           int max_phis_for_select = 0);
-
-  // Testing interface.
-  static Node* ReduceIfNodeForTesting(JSGraph* graph, Node* node);
-};
-}
-}
-}  // namespace v8::internal::compiler
-
-#endif  // V8_COMPILER_CONTROL_REDUCER_H_