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

src/compiler/pipeline-statistics.cc

Index: src/compiler/pipeline-statistics.cc
diff --git a/src/compiler/pipeline-statistics.cc b/src/compiler/pipeline-statistics.cc
index ba705ba1d8f8cc34df52a46aa3156ec800ecbae7..b98f837ee9714435922fb0208b3859b9b3650a50 100644
--- a/src/compiler/pipeline-statistics.cc
+++ b/src/compiler/pipeline-statistics.cc
@@ -36,7 +36,7 @@ void PipelineStatistics::CommonStats::End(
       diff->max_allocated_bytes_ + allocated_bytes_at_start_;
   diff->total_allocated_bytes_ =
       outer_zone_diff + scope_->GetTotalAllocatedBytes();
-  scope_.Reset(NULL);
+  scope_.Reset(nullptr);
   timer_.Stop();
 }
 
@@ -48,8 +48,8 @@ PipelineStatistics::PipelineStatistics(CompilationInfo* info,
       zone_pool_(zone_pool),
       compilation_stats_(isolate_->GetTurboStatistics()),
       source_size_(0),
-      phase_kind_name_(NULL),
-      phase_name_(NULL) {
+      phase_kind_name_(nullptr),
+      phase_name_(nullptr) {
   if (info->has_shared_info()) {
     source_size_ = static_cast<size_t>(info->shared_info()->SourceSize());
     base::SmartArrayPointer<char> name =