Support old-space allocation in generated code (bump block only for now).

runtime/vm/heap.h

Index: runtime/vm/heap.h
===================================================================
--- runtime/vm/heap.h	(revision 40250)
+++ runtime/vm/heap.h	(working copy)
@@ -145,10 +145,9 @@
   }
 
   // Accessors for inlined allocation in generated code.
-  uword TopAddress();
-  uword EndAddress();
-  static intptr_t new_space_offset() { return OFFSET_OF(Heap, new_space_); }
-  uword NewSpaceAddress() const { return reinterpret_cast<uword>(new_space_); }
+  uword TopAddress(Space space);
+  uword EndAddress(Space space);
+  Space SpaceForAllocation(intptr_t class_id) const;
 
   // Initialize the heap and register it with the isolate.
   static void Init(Isolate* isolate,