Last snapshot bits to get working precompiled hello_world on x64.

runtime/vm/virtual_memory.h

Index: runtime/vm/virtual_memory.h
diff --git a/runtime/vm/virtual_memory.h b/runtime/vm/virtual_memory.h
index 607e6b2b00553bcffc02f82149a748929fc9ebf8..44f34910e891741487816ce99bf05c66b6c6c45b 100644
--- a/runtime/vm/virtual_memory.h
+++ b/runtime/vm/virtual_memory.h
@@ -69,6 +69,8 @@ class VirtualMemory {
   // Commit a reserved memory area, so that the memory can be accessed.
   bool Commit(uword addr, intptr_t size, bool is_executable);
 
+  static VirtualMemory* ForInstructionsSnapshot(void* pointer, uword size);
+
  private:
   static VirtualMemory* ReserveInternal(intptr_t size);