1. Figure out the modified libraries from the specifeid kernel file during

runtime/vm/unit_test.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/unit_test.h"
 
 #include <stdio.h>
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
@@ skipping 196 matching lines @@
   }
   return NULL;
 }
 
 static Dart_Handle LibraryTagHandler(Dart_LibraryTag tag,
                                      Dart_Handle library,
                                      Dart_Handle url) {
   if (FLAG_use_dart_frontend) {
     // Reload request.
 
+    ASSERT(tag == Dart_kKernelTag);
     const char* urlstr = NULL;
     Dart_Handle result = Dart_StringToCString(url, &urlstr);
     if (Dart_IsError(result)) {
       return Dart_NewApiError("accessing url characters failed");
     }
 
     // Updated library either arrives as dart source or as
     // a precompiled kernel binary.
     void* kernel_pgm;
     if (script_reload_key != kUnsetThreadLocalKey) {
       const char* script_source = reinterpret_cast<const char*>(
           OSThread::GetThreadLocal(script_reload_key));
       ASSERT(script_source != NULL);
       OSThread::SetThreadLocal(script_reload_key, 0);
       char* error = TestCase::CompileTestScriptWithDFE(urlstr, script_source,
                                                        &kernel_pgm);
       if (error != NULL) {
         return Dart_NewApiError(error);
       }
     } else {
       ASSERT(kernel_reload_key != kUnsetThreadLocalKey);
       kernel_pgm =
           reinterpret_cast<void*>(OSThread::GetThreadLocal(kernel_reload_key));
-      ASSERT(kernel_pgm != NULL);
       OSThread::SetThreadLocal(kernel_reload_key, 0);
     }
-    return Dart_LoadScript(url, Dart_Null(),
-                           reinterpret_cast<Dart_Handle>(kernel_pgm), 0, 0);
+    ASSERT(kernel_pgm != NULL);
+    return Dart_NewExternalTypedData(Dart_TypedData_kUint64, kernel_pgm, 1);
   }
   if (tag == Dart_kCanonicalizeUrl) {
     Dart_Handle library_url = Dart_LibraryUrl(library);
     if (Dart_IsError(library_url)) {
       return library_url;
     }
     return Dart_DefaultCanonicalizeUrl(library_url, url);
   }
   if (tag == Dart_kScriptTag) {
     // Reload request.
@@ skipping 367 matching lines @@
     pos = strstr(in, prefix);
   }
   // Copy the remainder of in to out.
   while (*in != '\0') {
     *out++ = *in++;
   }
   *out = '\0';
 }
 
 }  // namespace dart