Add framework for Dart_Terminate which will cleanup stuff on exit.

runtime/bin/main.cc

Index: runtime/bin/main.cc
===================================================================
--- runtime/bin/main.cc	(revision 28185)
+++ runtime/bin/main.cc	(working copy)
@@ -630,6 +630,8 @@
   Dart_ExitScope();
   Dart_ShutdownIsolate();
 
+  Dart_Cleanup();
+
   return exit_code;
 }
 
@@ -799,8 +801,6 @@
     result = Dart_CreateScriptSnapshot(&buffer, &size);
     if (Dart_IsError(result)) {
       Log::PrintErr("%s\n", Dart_GetError(result));
-      Dart_ExitScope();
-      Dart_ShutdownIsolate();
       return DartErrorExit(result);
     }
 
@@ -875,6 +875,8 @@
   // Terminate process exit-code handler.
   Process::TerminateExitCodeHandler();
 
+  Dart_Cleanup();
+
   // Free copied argument strings if converted.
   if (argv_converted) {
     for (int i = 0; i < argc; i++) free(argv[i]);