Implement constructor and destructor of 64-bit assembler

src/x64/assembler-x64.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 859 matching lines @@
 
   friend class CodePatcher;
   friend class EnsureSpace;
 
   // Code buffer:
   // The buffer into which code and relocation info are generated.
   byte* buffer_;
   int buffer_size_;
   // True if the assembler owns the buffer, false if buffer is external.
   bool own_buffer_;
+  // A previously allocated buffer of kMinimalBufferSize bytes, or NULL.
+  static byte* spare_buffer_;
 
   // code generation
   byte* pc_;  // the program counter; moves forward
   RelocInfoWriter reloc_info_writer;
 
   // push-pop elimination
   byte* last_pc_;
 
   // source position information
   int current_statement_position_;
@@ skipping 26 matching lines @@
  private:
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_ASSEMBLER_X64_H_