- Add the ability to protect VirtualMemory.

runtime/vm/pages.h

Index: runtime/vm/pages.h
===================================================================
--- runtime/vm/pages.h	(revision 9969)
+++ runtime/vm/pages.h	(working copy)
@@ -57,6 +57,8 @@
 
   RawObject* FindObject(FindObjectVisitor* visitor) const;
 
+  void WriteProtect(bool read_only);
+
  private:
   static HeapPage* Initialize(VirtualMemory* memory, bool is_executable);
   static HeapPage* Allocate(intptr_t size, bool is_executable);
@@ -193,6 +195,8 @@
     page_space_controller_.Enable();
   }
 
+  void WriteProtect(bool read_only);
+
  private:
   static const intptr_t kAllocatablePageSize = kPageSize - sizeof(HeapPage);