Last snapshot bits to get working precompiled hello_world on x64.

runtime/vm/dart.h

Index: runtime/vm/dart.h
diff --git a/runtime/vm/dart.h b/runtime/vm/dart.h
index c0203cc4040b0c0cfcb1541fb7fbbfeb7ae92c00..5ae05507c71ef9613cd8347455989ffcb590439d 100644
--- a/runtime/vm/dart.h
+++ b/runtime/vm/dart.h
@@ -54,6 +54,16 @@ class Dart : public AllStatic {
   static uword AllocateReadOnlyHandle();
   static bool IsReadOnlyHandle(uword address);
 
+  static const uint8_t* instructions_snapshot_buffer() {
+    return instructions_snapshot_buffer_;
+  }
+  static void set_instructions_snapshot_buffer(const uint8_t* buffer) {
+    instructions_snapshot_buffer_ = buffer;
+  }
+  static bool IsRunningPrecompiledCode() {
+    return instructions_snapshot_buffer_ != NULL;
+  }
+
  private:
   static void WaitForIsolateShutdown();
 
@@ -61,6 +71,7 @@ class Dart : public AllStatic {
   static ThreadPool* thread_pool_;
   static DebugInfo* pprof_symbol_generator_;
   static ReadOnlyHandles* predefined_handles_;
+  static const uint8_t* instructions_snapshot_buffer_;
 };
 
 }  // namespace dart