Fix spacing and make functions const.

Author: adityamandaleeka

src/hotspot/share/gc/shared/collectedHeap.hpp

@@ -244,8 +244,8 @@ class CollectedHeap : public CHeapObj<mtInternal> {
   virtual size_t unused() const;
 
   // Historic gc information
-  size_t free_at_last_gc()    { return _capacity_at_last_gc - _used_at_last_gc; }
-  size_t used_at_last_gc()    { return _used_at_last_gc; }
+  size_t free_at_last_gc() const { return _capacity_at_last_gc - _used_at_last_gc; }
+  size_t used_at_last_gc() const { return _used_at_last_gc; }
   void update_capacity_and_used_at_gc();
 
   // Return "true" if the part of the heap that allocates Java