Fix remaining warnings.

lib/compiler/implementation/ssa/optimize.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 interface OptimizationPhase {
   String get name();
   void visitGraph(HGraph graph);
 }
 
 class SsaOptimizerTask extends CompilerTask {
@@ skipping 60 matching lines @@
  * If both inputs to known operations are available execute the operation at
  * compile-time.
  */
 class SsaConstantFolder extends HBaseVisitor implements OptimizationPhase {
   final String name = "SsaConstantFolder";
   final Compiler compiler;
   HGraph graph;
 
   SsaConstantFolder(this.compiler);
 
-  void visitGraph(HGraph graph) {
-    this.graph = graph;
-    visitDominatorTree(graph);
+  void visitGraph(HGraph visitee) {
+    graph = visitee;
+    visitDominatorTree(visitee);
   }
 
   visitBasicBlock(HBasicBlock block) {
     HInstruction instruction = block.first;
     while (instruction !== null) {
       HInstruction next = instruction.next;
       HInstruction replacement = instruction.accept(this);
       if (replacement !== instruction) {
         if (!replacement.isInBasicBlock()) {
           // The constant folding can return an instruction that is already
@@ skipping 618 matching lines @@
         }
       }
       if (!canBeMoved) continue;
 
       // This is safe because we are running after GVN.
       // TODO(ngeoffray): ensure GVN has been run.
       set_.add(current);
     }
   }
 }