message: Expose multi output fusion fuel to derived classes
  A derived class can do fusion in DoProducerConsumerMultiOutputFusion so
  we have to make sure it can correctly update the fusion fuel as well.
diff: @@ -104,17 +104,17 @@ class MultiOutputFusion : public HloPassInterface {
  // InstructionFusion instead.
  virtual bool DoProducerConsumerMultiOutputFusion();
  - private:
  - // Update the internal data structures after instr1 and instr2 are fused into
  - // one fusion instruction.
  - void Update(HloInstruction* instr1, HloInstruction* instr2);
  -
  // Optimization fuel is a compiler debugging technique that makes an
  // optimization pass stop what it is doing after having made N changes to the
  // program, where N is the fuel. By varying N, this can be used to find the
  // first single change that makes a test fail.
  int64 fuel_;
  + private:
  + // Update the internal data structures after instr1 and instr2 are fused into
  + // one fusion instruction.
  + void Update(HloInstruction* instr1, HloInstruction* instr2);
  +
  // Computation for the pass.
  HloComputation* computation_;
  