8236073: G1: Use SoftMaxHeapSize to guide GC heuristics

*** 43,60 ****
--- 43,62 ----
  
  class HeapRegion;
  class G1CollectionSet;
  class G1CollectionSetCandidates;
  class G1CollectionSetChooser;
+ class G1HeapSizingPolicy;
  class G1IHOPControl;
  class G1Analytics;
  class G1SurvivorRegions;
  class G1YoungGenSizer;
  class GCPolicyCounters;
  class STWGCTimer;
  
  class G1Policy: public CHeapObj<mtGC> {
+  friend class G1HeapSizingPolicy;
   private:
  
    static G1IHOPControl* create_ihop_control(const G1Predictions* predictor);
    // Update the IHOP control with necessary statistics.
    void update_ihop_prediction(double mutator_time_s,