[turbofan] Move graph trimming functionality to dedicated GraphTrimmer.

src/compiler/graph-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_GRAPH_REDUCER_H_
 #define V8_COMPILER_GRAPH_REDUCER_H_
 
 #include "src/compiler/node-marker.h"
 #include "src/zone-containers.h"
 
@@ skipping 29 matching lines @@
 // language-specific reductions (e.g. reduction based on types or constant
 // folding of low-level operators) can be integrated into the graph reduction
 // phase.
 class Reducer {
  public:
   virtual ~Reducer() {}
 
   // Try to reduce a node if possible.
   virtual Reduction Reduce(Node* node) = 0;
 
-  // Ask this reducer to finish operation, returns {true} if the reducer is
-  // done, while {false} indicates that the graph might need to be reduced
-  // again.
-  // TODO(turbofan): Remove this once the dead node trimming is in the
-  // GraphReducer.
-  virtual bool Finish();
-
   // Helper functions for subclasses to produce reductions for a node.
   static Reduction NoChange() { return Reduction(); }
   static Reduction Replace(Node* node) { return Reduction(node); }
   static Reduction Changed(Node* node) { return Reduction(node); }
 };
 
 
 // An advanced reducer can also edit the graphs by changing and replacing nodes
 // other than the one currently being reduced.
 class AdvancedReducer : public Reducer {
@@ skipping 112 matching lines @@
   ZoneStack<NodeState> stack_;
 
   DISALLOW_COPY_AND_ASSIGN(GraphReducer);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_GRAPH_REDUCER_H_