Fix presubmit error with explicit constructor in test.

test/cctest/compiler/test-simplified-lowering.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 <limits>
 
 #include "src/compiler/control-builders.h"
 #include "src/compiler/generic-node-inl.h"
 #include "src/compiler/graph-visualizer.h"
 #include "src/compiler/node-properties-inl.h"
@@ skipping 596 matching lines @@
 class TestingGraph : public HandleAndZoneScope, public GraphAndBuilders {
  public:
   Typer typer;
   JSGraph jsgraph;
   Node* p0;
   Node* p1;
   Node* start;
   Node* end;
   Node* ret;
 
-  TestingGraph(Type* p0_type, Type* p1_type = Type::None())
+  explicit TestingGraph(Type* p0_type, Type* p1_type = Type::None())
       : GraphAndBuilders(main_zone()),
         typer(main_zone()),
         jsgraph(graph(), common(), &typer) {
     start = graph()->NewNode(common()->Start(2));
     graph()->SetStart(start);
     ret =
         graph()->NewNode(common()->Return(), jsgraph.Constant(0), start, start);
     end = graph()->NewNode(common()->End(), ret);
     graph()->SetEnd(end);
     p0 = graph()->NewNode(common()->Parameter(0), start);
@@ skipping 735 matching lines @@
 
   Node* store = t.graph()->NewNode(t.simplified()->StoreField(access), t.p0,
                                    t.p1, t.start, t.start);
   t.Effect(store);
   t.Lower();
 
   CHECK_EQ(IrOpcode::kStore, store->opcode());
   CHECK_EQ(t.p0, store->InputAt(0));
   CheckChangeOf(IrOpcode::kChangeTaggedToFloat64, t.p1, store->InputAt(2));
 }