[turbofan] Turn LoadElimination into an AdvancedReducer.

test/unittests/compiler/load-elimination-unittest.cc

 // 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.
 
 #include "src/compiler/access-builder.h"
 #include "src/compiler/load-elimination.h"
 #include "src/compiler/simplified-operator.h"
 #include "test/unittests/compiler/graph-unittest.h"
 #include "test/unittests/compiler/node-test-utils.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 class LoadEliminationTest : public GraphTest {
  public:
   LoadEliminationTest() : GraphTest(3), simplified_(zone()) {}
   ~LoadEliminationTest() override {}
 
  protected:
   Reduction Reduce(Node* node) {
-    LoadElimination reducer;
+    // TODO(titzer): mock the GraphReducer here for better unit testing.
+    GraphReducer graph_reducer(zone(), graph());
+    LoadElimination reducer(&graph_reducer);
     return reducer.Reduce(node);
   }
 
   SimplifiedOperatorBuilder* simplified() { return &simplified_; }
 
  private:
   SimplifiedOperatorBuilder simplified_;
 };
 
 
@@ skipping 30 matching lines @@
 
   Reduction r4 = Reduce(graph()->NewNode(simplified()->LoadField(access1),
                                          object1, store3, control));
   ASSERT_TRUE(r4.Changed());
   EXPECT_EQ(value, r4.replacement());
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8