- Add the ability to protect VirtualMemory.

runtime/vm/virtual_memory.h

Index: runtime/vm/virtual_memory.h
===================================================================
--- runtime/vm/virtual_memory.h	(revision 9969)
+++ runtime/vm/virtual_memory.h	(working copy)
@@ -13,6 +13,14 @@
 
 class VirtualMemory {
  public:
+  enum Protection {
+    kNoAccess,
+    kReadOnly,
+    kReadWrite,
+    kReadExecute,
+    kReadWriteExecute
+  };
+
   // The reserved memory is unmapped on destruction.
   ~VirtualMemory();
 
@@ -32,6 +40,9 @@
     return Commit(start(), size(), is_executable);
   }
 
+  // Changes the protection of the virtual memory area.
+  bool Protect(Protection mode);
+
   // Reserves a virtual memory segment with size. If a segment of the requested
   // size cannot be allocated NULL is returned.
   static VirtualMemory* Reserve(intptr_t size);