Fix presubmit errors.

src/x64/codegen-x64.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 330 matching lines @@
   CodeGenState* state() { return state_; }
   void set_state(CodeGenState* state) { state_ = state; }
 
   void AddDeferred(DeferredCode* code) { deferred_.Add(code); }
 
   bool in_spilled_code() const { return in_spilled_code_; }
   void set_in_spilled_code(bool flag) { in_spilled_code_ = flag; }
 
  private:
   // Construction/Destruction
-  CodeGenerator(MacroAssembler* masm);
+  explicit CodeGenerator(MacroAssembler* masm);
 
   // Accessors
   inline bool is_eval();
   Scope* scope();
 
   // Generating deferred code.
   void ProcessDeferred();
 
   // State
   ControlDestination* destination() const { return state_->destination(); }
@@ skipping 455 matching lines @@
   Major MajorKey() { return StringCompare; }
   int MinorKey() { return 0; }
 
   void Generate(MacroAssembler* masm);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_CODEGEN_X64_H_