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

src/compiler/frame.cc

 // Copyright 2015 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.
 
 #include "src/compiler/frame.h"
 
 #include "src/compiler/linkage.h"
 #include "src/compiler/register-allocator.h"
 #include "src/macro-assembler.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 Frame::Frame(int fixed_frame_size_in_slots, const CallDescriptor* descriptor)
     : needs_frame_((descriptor != nullptr) &&
                    descriptor->RequiresFrameAsIncoming()),
       frame_slot_count_(fixed_frame_size_in_slots),
       callee_saved_slot_count_(0),
       spill_slot_count_(0),
-      allocated_registers_(NULL),
-      allocated_double_registers_(NULL) {}
+      allocated_registers_(nullptr),
+      allocated_double_registers_(nullptr) {}
 
 
 void FrameAccessState::SetFrameAccessToDefault() {
   if (frame()->needs_frame() && !FLAG_turbo_sp_frame_access) {
     SetFrameAccessToFP();
   } else {
     SetFrameAccessToSP();
   }
 }
 
@@ skipping 10 matching lines @@
     int sp_offset =
         offset + ((frame()->GetSpToFpSlotCount() + sp_delta()) * kPointerSize);
     return FrameOffset::FromStackPointer(sp_offset);
   }
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8