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

runtime/vm/snapshot_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 "include/dart_debugger_api.h"
 #include "platform/assert.h"
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_api_message.h"
@@ skipping 945 matching lines @@
     Dart_ExitScope();
   }
 
   {
     // Create an Isolate using the full snapshot, load a script and create
     // a script snapshot of the script.
     TestCase::CreateTestIsolateFromSnapshot(full_snapshot);
     Dart_EnterScope();  // Start a Dart API scope for invoking API functions.
 
     // Load the library.
-    Dart_Handle import_map = Dart_NewList(0);
     Dart_Handle import_lib = Dart_LoadLibrary(Dart_NewString("dart:import-lib"),
-                                              Dart_NewString(kLibScriptChars),
-                                              import_map);
+                                              Dart_NewString(kLibScriptChars));
     EXPECT_VALID(import_lib);
 
     // Create a test library and Load up a test script in it.
     TestCase::LoadTestScript(kScriptChars, NULL);
 
     EXPECT_VALID(Dart_LibraryImportLibrary(TestCase::lib(), import_lib));
 
     // Get list of library URLs loaded and save the count.
     Dart_Handle libs = Dart_GetLibraryURLs();
     EXPECT(Dart_IsList(libs));
@@ skipping 548 matching lines @@
   EXPECT(Dart_ErrorHasException(result));
   EXPECT_SUBSTRING("Exception: nulltruefalse1234563.14[]100123456789\n",
                    Dart_GetError(result));
 
   Dart_ExitScope();
 }
 
 #endif  // defined(TARGET_ARCH_IA32) || defined(TARGET_ARCH_X64).
 
 }  // namespace dart