Only reload libraries when they may have been modified.

runtime/bin/builtin.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 <stdio.h>
 
 #include "include/dart_api.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
@@ skipping 101 matching lines @@
 
 void Builtin::SetNativeResolver(BuiltinLibraryId id) {
   UNREACHABLE();
 }
 
 
 Dart_Handle Builtin::LoadLibrary(Dart_Handle url, BuiltinLibraryId id) {
   ASSERT(static_cast<int>(id) >= 0);
   ASSERT(static_cast<int>(id) < num_libs_);
 
-  Dart_Handle library = Dart_LoadLibrary(url, Source(id), 0, 0);
+  Dart_Handle library = Dart_LoadLibrary(url, Dart_Null(), Source(id), 0, 0);
   if (!Dart_IsError(library) && (builtin_libraries_[id].has_natives_)) {
     // Setup the native resolver for built in library functions.
     DART_CHECK_VALID(
         Dart_SetNativeResolver(library, NativeLookup, NativeSymbol));
   }
   if (builtin_libraries_[id].patch_url_ != NULL) {
     ASSERT(builtin_libraries_[id].patch_paths_ != NULL);
     LoadPatchFiles(library,
                    builtin_libraries_[id].patch_url_,
                    builtin_libraries_[id].patch_paths_);
@@ skipping 23 matching lines @@
   Dart_Handle url = DartUtils::NewString(builtin_libraries_[id].url_);
   Dart_Handle library = Dart_LookupLibrary(url);
   if (Dart_IsError(library)) {
     library = LoadLibrary(url, id);
   }
   return library;
 }
 
 }  // namespace bin
 }  // namespace dart