MIPS: Fix bad RegisterConfiguration usage in InstructionSequence unit tests.

test/unittests/compiler/instruction-sequence-unittest.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_UNITTESTS_COMPILER_INSTRUCTION_SEQUENCE_UNITTEST_H_
 #define V8_UNITTESTS_COMPILER_INSTRUCTION_SEQUENCE_UNITTEST_H_
 
 #include <memory>
 
 #include "src/compiler/instruction.h"
@@ skipping 138 matching lines @@
   static BlockCompletion Last() {
     BlockCompletion completion = {kBlockEnd, TestOperand(), kNoValue, kNoValue};
     return completion;
   }
 
   InstructionSequenceTest();
 
   void SetNumRegs(int num_general_registers, int num_double_registers);
   int GetNumRegs(MachineRepresentation rep);
   int GetAllocatableCode(int index, MachineRepresentation rep = kNoRep);
-  RegisterConfiguration* config();
+  const RegisterConfiguration* config();
   InstructionSequence* sequence();
 
   void StartLoop(int loop_blocks);
   void EndLoop();
   void StartBlock(bool deferred = false);
   Instruction* EndBlock(BlockCompletion completion = FallThrough());
 
   TestOperand Imm(int32_t imm = 0);
   VReg Define(TestOperand output_op);
   VReg Parameter(TestOperand output_op = Reg()) { return Define(output_op); }
@@ skipping 115 matching lines @@
   bool block_returns_;
 
   DISALLOW_COPY_AND_ASSIGN(InstructionSequenceTest);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_UNITTESTS_COMPILER_INSTRUCTION_SEQUENCE_UNITTEST_H_