When building standalone Dart executable, put implementation of dart:io natives in a separate libra…

runtime/bin/builtin_gen_snapshot.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 12 matching lines @@
 
 
 Dart_Handle Builtin::Source(BuiltinLibraryId id) {
   ASSERT((sizeof(builtin_libraries_) / sizeof(builtin_lib_props)) ==
          kInvalidLibrary);
   ASSERT(id >= kBuiltinLibrary && id < kInvalidLibrary);
   return DartUtils::NewString(builtin_libraries_[id].source_);
 }
 
 
+Dart_NativeFunction Builtin::NativeLookup(Dart_Handle name,
+                                          int argument_count) {
+  UNREACHABLE();
+  return NULL;
+}
+
+
 void Builtin::SetNativeResolver(BuiltinLibraryId id) {
   UNREACHABLE();
 }
 
 
 Dart_Handle Builtin::LoadAndCheckLibrary(BuiltinLibraryId id) {
   ASSERT((sizeof(builtin_libraries_) / sizeof(builtin_lib_props)) ==
          kInvalidLibrary);
   ASSERT(id >= kBuiltinLibrary && id < kInvalidLibrary);
   Dart_Handle url = DartUtils::NewString(builtin_libraries_[id].url_);
   Dart_Handle library = Dart_LookupLibrary(url);
   if (Dart_IsError(library)) {
     library = Dart_LoadLibrary(url, Source(id));
     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));
+      // Looks up native functions only in libdart_builtin, not libdart_io.
+      // This is for use in the snapshot generator, which should be
+      // independent of most of the dart:io C++ code.
+      DART_CHECK_VALID(Dart_SetNativeResolver(library, BuiltinNativeLookup));
     }
     if (builtin_libraries_[id].patch_url_ != NULL) {
       ASSERT(builtin_libraries_[id].patch_source_ != NULL);
       Dart_Handle patch_url =
           DartUtils::NewString(builtin_libraries_[id].patch_url_);
       Dart_Handle patch_source =
           DartUtils::NewString(builtin_libraries_[id].patch_source_);
       DART_CHECK_VALID(Dart_LoadPatch(library, patch_url, patch_source));
     }
   }
   DART_CHECK_VALID(library);
   return library;
 }