Implement spawnUri from dart:isolate. This function allows us to

runtime/bin/dartutils.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 "bin/dartutils.h"
 
 #include "bin/file.h"
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/globals.h"
@@ skipping 181 matching lines @@
   Dart_Handle str = Dart_NewString(text_buffer);
   free(text_buffer);
   return str;
 }
 
 
 Dart_Handle DartUtils::LoadSource(CommandLineOptions* url_mapping,
                                   Dart_Handle library,
                                   Dart_Handle url,
                                   Dart_LibraryTag tag,
-                                  const char* url_string,
-                                  Dart_Handle import_map) {
+                                  const char* url_string) {
   if (url_mapping != NULL && IsDartSchemeURL(url_string)) {
     const char* mapped_url_string = MapLibraryUrl(url_mapping, url_string);
     if (mapped_url_string == NULL) {
       return Dart_Error("Do not know how to load %s", url_string);
     }
     // We have a URL mapping specified, just read the file that the
     // URL mapping specifies and load it.
     url_string = mapped_url_string;
   }
   // The tag is either an import or a source tag.
   // Read the file and load it according to the specified tag.
   Dart_Handle source = DartUtils::ReadStringFromFile(url_string);
   if (Dart_IsError(source)) {
     return source;  // source contains the error string.
   }
   if (tag == kImportTag) {
     // Return library object or an error string.
-    return Dart_LoadLibrary(url, source, import_map);
+    return Dart_LoadLibrary(url, source);
   } else if (tag == kSourceTag) {
     return Dart_LoadSource(library, url, source);
   }
   return Dart_Error("wrong tag");
 }
 
 
 const char* DartUtils::GetCanonicalPath(const char* reference_dir,
                                         const char* filename) {
   if (File::IsAbsolutePath(filename)) {
@@ skipping 201 matching lines @@
 
 CObject* CObject::NewOSError(OSError* os_error) {
   CObject* error_message =
       new CObjectString(CObject::NewString(os_error->message()));
   CObjectArray* result = new CObjectArray(CObject::NewArray(3));
   result->SetAt(0, new CObjectInt32(CObject::NewInt32(kOSError)));
   result->SetAt(1, new CObjectInt32(CObject::NewInt32(os_error->code())));
   result->SetAt(2, error_message);
   return result;
 }