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

src/compiler/control-builders.h

Index: src/compiler/control-builders.h
diff --git a/src/compiler/control-builders.h b/src/compiler/control-builders.h
index 0c2fa739361c4b4bd0b355aa9e7cac14525c9265..6ff00be59614378dd8be96943bbe77ba5e35479d 100644
--- a/src/compiler/control-builders.h
+++ b/src/compiler/control-builders.h
@@ -41,8 +41,8 @@ class IfBuilder final : public ControlBuilder {
  public:
   explicit IfBuilder(AstGraphBuilder* builder)
       : ControlBuilder(builder),
-        then_environment_(NULL),
-        else_environment_(NULL) {}
+        then_environment_(nullptr),
+        else_environment_(nullptr) {}
 
   // Primitive control commands.
   void If(Node* condition, BranchHint hint = BranchHint::kNone);
@@ -61,9 +61,9 @@ class LoopBuilder final : public ControlBuilder {
  public:
   explicit LoopBuilder(AstGraphBuilder* builder)
       : ControlBuilder(builder),
-        loop_environment_(NULL),
-        continue_environment_(NULL),
-        break_environment_(NULL) {}
+        loop_environment_(nullptr),
+        continue_environment_(nullptr),
+        break_environment_(nullptr) {}
 
   // Primitive control commands.
   void BeginLoop(BitVector* assigned, bool is_osr = false);
@@ -90,9 +90,9 @@ class SwitchBuilder final : public ControlBuilder {
  public:
   explicit SwitchBuilder(AstGraphBuilder* builder, int case_count)
       : ControlBuilder(builder),
-        body_environment_(NULL),
-        label_environment_(NULL),
-        break_environment_(NULL),
+        body_environment_(nullptr),
+        label_environment_(nullptr),
+        break_environment_(nullptr),
         body_environments_(case_count, zone()) {}
 
   // Primitive control commands.
@@ -122,7 +122,7 @@ class SwitchBuilder final : public ControlBuilder {
 class BlockBuilder final : public ControlBuilder {
  public:
   explicit BlockBuilder(AstGraphBuilder* builder)
-      : ControlBuilder(builder), break_environment_(NULL) {}
+      : ControlBuilder(builder), break_environment_(nullptr) {}
 
   // Primitive control commands.
   void BeginBlock();
@@ -145,9 +145,9 @@ class TryCatchBuilder final : public ControlBuilder {
  public:
   explicit TryCatchBuilder(AstGraphBuilder* builder)
       : ControlBuilder(builder),
-        catch_environment_(NULL),
-        exit_environment_(NULL),
-        exception_node_(NULL) {}
+        catch_environment_(nullptr),
+        exit_environment_(nullptr),
+        exception_node_(nullptr) {}
 
   // Primitive control commands.
   void BeginTry();
@@ -170,9 +170,9 @@ class TryFinallyBuilder final : public ControlBuilder {
  public:
   explicit TryFinallyBuilder(AstGraphBuilder* builder)
       : ControlBuilder(builder),
-        finally_environment_(NULL),
-        token_node_(NULL),
-        value_node_(NULL) {}
+        finally_environment_(nullptr),
+        token_node_(nullptr),
+        value_node_(nullptr) {}
 
   // Primitive control commands.
   void BeginTry();