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

src/compiler/ast-loop-assignment-analyzer.h

Index: src/compiler/ast-loop-assignment-analyzer.h
diff --git a/src/compiler/ast-loop-assignment-analyzer.h b/src/compiler/ast-loop-assignment-analyzer.h
index 7bb29bbb0c1c20f6657946eac71fd15925c89acc..169691135a97bce8ee00ae2f64c9590bb48160eb 100644
--- a/src/compiler/ast-loop-assignment-analyzer.h
+++ b/src/compiler/ast-loop-assignment-analyzer.h
@@ -26,7 +26,7 @@ class LoopAssignmentAnalysis : public ZoneObject {
       if (list_[i].first == loop) return list_[i].second;
     }
     UNREACHABLE();  // should never ask for loops that aren't here!
-    return NULL;
+    return nullptr;
   }
 
   int GetAssignmentCountForTesting(Scope* scope, Variable* var);
@@ -63,7 +63,7 @@ class AstLoopAssignmentAnalyzer : public AstVisitor {
   void Exit(IterationStatement* loop);
 
   void VisitIfNotNull(AstNode* node) {
-    if (node != NULL) Visit(node);
+    if (node != nullptr) Visit(node);
   }
 
   void AnalyzeAssignment(Variable* var);