Remove assumption from the heap verifier that objects occupy a narrow range of the address space.

runtime/vm/pages.h

Index: runtime/vm/pages.h
diff --git a/runtime/vm/pages.h b/runtime/vm/pages.h
index ae32c87066ee3e5b20066535a881e646c73e4fef..640e771f30036d72e087d96c76f6715efc9689d0 100644
--- a/runtime/vm/pages.h
+++ b/runtime/vm/pages.h
@@ -23,6 +23,7 @@ DECLARE_FLAG(bool, write_protect_code);
 class Heap;
 class JSONObject;
 class ObjectPointerVisitor;
+class ObjectSet;
 
 // A page containing old generation objects.
 class HeapPage {
@@ -269,7 +270,7 @@ class PageSpace {
   // Collect the garbage in the page space using mark-sweep.
   void MarkSweep(bool invoke_api_callbacks);
 
-  void StartEndAddress(uword* start, uword* end) const;
+  void AddRegionsToObjectSet(ObjectSet* set) const;
 
   void InitGrowthControl() {
     page_space_controller_.set_last_usage(usage_);