Refactor ExternalReference::isolate_address() to not rely on Isolate::Current().

src/x64/regexp-macro-assembler-x64.h

 // Copyright 2012 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 254 matching lines @@
   inline void Push(Label* label);
 
   // Pops a value from the backtrack stack. Reads the word at the stack pointer
   // (rcx) and increments it by a word size.
   inline void Pop(Register target);
 
   // Drops the top value from the backtrack stack without reading it.
   // Increments the stack pointer (rcx) by a word size.
   inline void Drop();
 
+  Isolate* isolate() const { return masm_.isolate(); }
+
   MacroAssembler masm_;
   MacroAssembler::NoRootArrayScope no_root_array_scope_;
 
   ZoneList<int> code_relative_fixup_positions_;
 
   // Which mode to generate code for (ASCII or UC16).
   Mode mode_;
 
   // One greater than maximal register index actually used.
   int num_registers_;
@@ skipping 10 matching lines @@
   Label exit_label_;
   Label check_preempt_label_;
   Label stack_overflow_label_;
 };
 
 #endif  // V8_INTERPRETED_REGEXP
 
 }}  // namespace v8::internal
 
 #endif  // V8_X64_REGEXP_MACRO_ASSEMBLER_X64_H_