Unbreak MIPS build after recent zone-related changes

src/mips/lithium-mips.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 2234 matching lines @@
   ZoneList<Handle<JSFunction> > inlined_closures_;
 };
 
 
 class LChunkBuilder BASE_EMBEDDED {
  public:
   LChunkBuilder(CompilationInfo* info, HGraph* graph, LAllocator* allocator)
       : chunk_(NULL),
         info_(info),
         graph_(graph),
-        zone_(graph->isolate()->zone()),
+        zone_(graph->zone()),
         status_(UNUSED),
         current_instruction_(NULL),
         current_block_(NULL),
         next_block_(NULL),
         argument_count_(0),
         allocator_(allocator),
         position_(RelocInfo::kNoPosition),
         instruction_pending_deoptimization_environment_(NULL),
         pending_deoptimization_ast_id_(AstNode::kNoNumber) { }
 
@@ skipping 130 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_MIPS_LITHIUM_MIPS_H_