Lazy peer API.

runtime/vm/pages.h

Index: runtime/vm/pages.h
diff --git a/runtime/vm/pages.h b/runtime/vm/pages.h
index 83a07ddc0ffc45f2d10652dddbb95a43ce948474..48b216f71e877748c1583ca56e876d8adc3a4ade 100644
--- a/runtime/vm/pages.h
+++ b/runtime/vm/pages.h
@@ -5,6 +5,8 @@
 #ifndef VM_PAGES_H_
 #define VM_PAGES_H_
 
+#include <map>
+
 #include "vm/freelist.h"
 #include "vm/globals.h"
 #include "vm/virtual_memory.h"
@@ -201,6 +203,16 @@ class PageSpace {
 
   void WriteProtect(bool read_only);
 
+  typedef std::map<RawObject*, void*> PeerTable;
+
+  void SetPeer(RawObject* raw_obj, void* peer);
+
+  void* GetPeer(RawObject* raw_obj);
+
+  int64_t PeerCount() const;
+
+  PeerTable* GetPeerTable() { return &peer_table_; }
+
  private:
   static const intptr_t kAllocatablePageSize = kPageSize - sizeof(HeapPage);
 
@@ -227,6 +239,8 @@ class PageSpace {
   HeapPage* pages_tail_;
   HeapPage* large_pages_;
 
+  PeerTable peer_table_;
+
   // Page being used for bump allocation.
   // The value has different meanings:
   // NULL: Still bump allocating from last allocated fresh page.