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

src/compiler/arm64/code-generator-arm64.cc

Index: src/compiler/arm64/code-generator-arm64.cc
diff --git a/src/compiler/arm64/code-generator-arm64.cc b/src/compiler/arm64/code-generator-arm64.cc
index aa5f309fc2f12b047e41f08805f770922a2ef096..6a508a10c04e0cf1917a5650b3e04e72e7c4ba72 100644
--- a/src/compiler/arm64/code-generator-arm64.cc
+++ b/src/compiler/arm64/code-generator-arm64.cc
@@ -205,7 +205,7 @@ class Arm64OperandConverter final : public InstructionOperandConverter {
   }
 
   MemOperand ToMemOperand(InstructionOperand* op, MacroAssembler* masm) const {
-    DCHECK(op != NULL);
+    DCHECK_NOT_NULL(op);
     DCHECK(op->IsStackSlot() || op->IsDoubleStackSlot());
     FrameOffset offset = frame_access_state()->GetFrameOffset(
         AllocatedOperand::cast(op)->index());
@@ -1461,7 +1461,7 @@ void CodeGenerator::AssembleReturn() {
 
 void CodeGenerator::AssembleMove(InstructionOperand* source,
                                  InstructionOperand* destination) {
-  Arm64OperandConverter g(this, NULL);
+  Arm64OperandConverter g(this, nullptr);
   // Dispatch on the source and destination operand kinds.  Not all
   // combinations are possible.
   if (source->IsRegister()) {
@@ -1558,7 +1558,7 @@ void CodeGenerator::AssembleMove(InstructionOperand* source,
 
 void CodeGenerator::AssembleSwap(InstructionOperand* source,
                                  InstructionOperand* destination) {
-  Arm64OperandConverter g(this, NULL);
+  Arm64OperandConverter g(this, nullptr);
   // Dispatch on the source and destination operand kinds.  Not all
   // combinations are possible.
   if (source->IsRegister()) {