[turbofan] Introduces a step to verify the machine graph.

src/compiler/machine-graph-verifier.h

+// Copyright 2016 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_MACHINE_GRAPH_VERIFIER_H_
+#define V8_COMPILER_MACHINE_GRAPH_VERIFIER_H_
+
+#include "src/base/macros.h"
+
+namespace v8 {
+namespace internal {
+class Zone;
+namespace compiler {
+
+class Graph;
+class Linkage;
+class Schedule;
+
+// Verifies properties of a scheduled graph, such as that the nodes' inputs are
+// of the correct type.
+class MachineGraphVerifier {
+ public:
+  static void Run(Graph* graph, Schedule const* const schedule,
+                  Linkage* linkage, Zone* temp_zone);
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_MACHINE_GRAPH_VERIFIER_H_