8236073: G1: Use SoftMaxHeapSize to guide GC heuristics

@@ -61,11 +61,16 @@
 // NewSize==MaxNewSize case above. But we will update the min and max
 // every time the heap size changes.
 //
 // NewSize and MaxNewSize override NewRatio. So, NewRatio is ignored if it is
 // combined with either NewSize or MaxNewSize. (A warning message is printed.)
+
+// Forward declarations
+class G1HeapSizingPolicy;
+
 class G1YoungGenSizer : public CHeapObj<mtGC> {
+  friend class G1HeapSizingPolicy;
 private:
   enum SizerKind {
     SizerDefaults,
     SizerNewSizeOnly,
     SizerMaxNewSizeOnly,