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

src/compiler/loop-analysis.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_LOOP_ANALYSIS_H_
 #define V8_COMPILER_LOOP_ANALYSIS_H_
 
 #include "src/base/iterator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/node.h"
@@ skipping 95 matching lines @@
                      &loop_nodes_[0] + loop->body_end_);
   }
 
   // Return the node that represents the control, i.e. the loop node itself.
   Node* GetLoopControl(Loop* loop) {
     // TODO(turbofan): make the loop control node always first?
     for (Node* node : HeaderNodes(loop)) {
       if (node->opcode() == IrOpcode::kLoop) return node;
     }
     UNREACHABLE();
-    return NULL;
+    return nullptr;
   }
 
  private:
   friend class LoopFinderImpl;
 
   Loop* NewLoop() {
     all_loops_.push_back(Loop(zone_));
     Loop* result = &all_loops_.back();
     return result;
   }
@@ skipping 20 matching lines @@
   // Build a loop tree for the entire graph.
   static LoopTree* BuildLoopTree(Graph* graph, Zone* temp_zone);
 };
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_LOOP_ANALYSIS_H_