Added option --script-snapshot in gen_snapshot to generate the snapshot of a scipt into the file.

runtime/bin/dartutils.h

Index: runtime/bin/dartutils.h
===================================================================
--- runtime/bin/dartutils.h	(revision 11672)
+++ runtime/bin/dartutils.h	(working copy)
@@ -90,6 +90,12 @@
                                      Dart_Handle library,
                                      const char* url_str);
   static Dart_Handle ReadStringFromFile(const char* filename);
+  static Dart_Handle LibraryTagHandler(Dart_LibraryTag tag,
+                                       Dart_Handle library,
+                                       Dart_Handle url);
+  static Dart_Handle LoadScript(const char* script_uri,
+                                bool resolve_script,
+                                Dart_Handle builtin_lib);
   static Dart_Handle LoadSource(CommandLineOptions* url_mapping,
                                 Dart_Handle library,
                                 Dart_Handle url,
@@ -103,6 +109,11 @@
   // Create a new Dart OSError object with the provided OS error.
   static Dart_Handle NewDartOSError(OSError* os_error);
 
+  static void SetOriginalWorkingDirectory();
+
+  // Global state that stores the original working directory..
+  static const char* original_working_directory;
+
   static const char* kDartScheme;
   static const char* kDartExtensionScheme;
   static const char* kBuiltinLibURL;