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

runtime/bin/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.
 
 // Generate a snapshot file after loading all the scripts specified on the
 // command line.
 
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
@@ skipping 98 matching lines @@
   ASSERT(file != NULL);
   for (intptr_t i = 0; i < size; i++) {
     file->WriteByte(buffer[i]);
   }
   delete file;
 }
 
 
 static Dart_Handle CreateSnapshotLibraryTagHandler(Dart_LibraryTag tag,
                                                    Dart_Handle library,
-                                                   Dart_Handle url,
-                                                   Dart_Handle import_map) {
+                                                   Dart_Handle url) {
   if (!Dart_IsLibrary(library)) {
     return Dart_Error("not a library");
   }
   if (!Dart_IsString8(url)) {
     return Dart_Error("url is not a string");
   }
   const char* url_string = NULL;
   Dart_Handle result = Dart_StringToCString(url, &url_string);
   if (Dart_IsError(result)) {
     return result;
   }
 
   // If the URL starts with "dart:" then it is handled specially.
   bool is_dart_scheme_url = DartUtils::IsDartSchemeURL(url_string);
   if (tag == kCanonicalizeUrl) {
     if (is_dart_scheme_url) {
       return url;
     }
     return DartUtils::CanonicalizeURL(url_mapping, library, url_string);
   }
   return DartUtils::LoadSource(url_mapping,
                                library,
                                url,
                                tag,
-                               url_string,
-                               import_map);
+                               url_string);
 }
 
 
 static Dart_Handle LoadSnapshotCreationScript(const char* script_name) {
   Dart_Handle source = DartUtils::ReadStringFromFile(script_name);
   if (Dart_IsError(source)) {
     return source;  // source contains the error string.
   }
   Dart_Handle url = Dart_NewString(script_name);
-  Dart_Handle import_map = Dart_NewList(0);
 
-  return Dart_LoadScript(url,
-                         source,
-                         import_map);
+  return Dart_LoadScript(url, source);
 }
 
 
 static Dart_Handle BuiltinLibraryTagHandler(Dart_LibraryTag tag,
                                             Dart_Handle library,
-                                            Dart_Handle url,
-                                            Dart_Handle import_map) {
+                                            Dart_Handle url) {
   if (!Dart_IsLibrary(library)) {
     return Dart_Error("not a library");
   }
   if (!Dart_IsString8(url)) {
     return Dart_Error("url is not a string");
   }
   const char* url_string = NULL;
   Dart_Handle result = Dart_StringToCString(url, &url_string);
   if (Dart_IsError(result)) {
     return result;
@@ skipping 77 matching lines @@
   }
 
   Dart_SetVMFlags(vm_options.count(), vm_options.arguments());
 
   // Initialize the Dart VM.
   // Note: We don't expect isolates to be created from dart code during
   // snapshot generation.
   Dart_Initialize(NULL, NULL);
 
   char* error;
-  Dart_Isolate isolate = Dart_CreateIsolate(NULL, NULL, NULL, &error);
+  Dart_Isolate isolate = Dart_CreateIsolate(NULL, NULL, NULL, NULL, &error);
   if (isolate == NULL) {
     fprintf(stderr, "%s", error);
     free(error);
     exit(255);
   }
 
   Dart_Handle result;
   Dart_Handle library;
   Dart_EnterScope();
 
@@ skipping 46 matching lines @@
     exit(255);
   }
   // Now write the snapshot out to specified file and exit.
   WriteSnapshotFile(buffer, size);
   Dart_ExitScope();
 
   // Shutdown the isolate.
   Dart_ShutdownIsolate();
   return 0;
 }