[turbofan] Build s/NULL/nullptr/g and CHECK(x != nullptr) to CHECK_NOT_NULL(x).

src/compiler/pipeline-statistics.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_PIPELINE_STATISTICS_H_
 #define V8_COMPILER_PIPELINE_STATISTICS_H_
 
 #include <string>
 
 #include "src/compilation-statistics.h"
@@ skipping 58 matching lines @@
   CommonStats phase_stats_;
 
   DISALLOW_COPY_AND_ASSIGN(PipelineStatistics);
 };
 
 
 class PhaseScope {
  public:
   PhaseScope(PipelineStatistics* pipeline_stats, const char* name)
       : pipeline_stats_(pipeline_stats) {
-    if (pipeline_stats_ != NULL) pipeline_stats_->BeginPhase(name);
+    if (pipeline_stats_ != nullptr) pipeline_stats_->BeginPhase(name);
   }
   ~PhaseScope() {
-    if (pipeline_stats_ != NULL) pipeline_stats_->EndPhase();
+    if (pipeline_stats_ != nullptr) pipeline_stats_->EndPhase();
   }
 
  private:
   PipelineStatistics* const pipeline_stats_;
 
   DISALLOW_COPY_AND_ASSIGN(PhaseScope);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif