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

runtime/vm/unit_test.h

 // Copyright (c) 2011, 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.
 
 #ifndef VM_UNIT_TEST_H_
 #define VM_UNIT_TEST_H_
 
 #include "include/dart_api.h"
 
 #include "vm/ast.h"
@@ skipping 163 matching lines @@
   static Dart_Handle lib();
   static const char* url() { return "dart:test-lib"; }
   static Dart_Isolate CreateTestIsolateFromSnapshot(uint8_t* buffer) {
     return CreateIsolate(buffer);
   }
   static Dart_Isolate CreateTestIsolate() {
     return CreateIsolate(NULL);
   }
   static Dart_Handle library_handler(Dart_LibraryTag tag,
                                      Dart_Handle library,
-                                     Dart_Handle url,
-                                     Dart_Handle import_map);
+                                     Dart_Handle url);
 
   virtual void Run();
 
  private:
   static Dart_Isolate CreateIsolate(uint8_t* buffer) {
     char* err;
-    Dart_Isolate isolate = Dart_CreateIsolate(NULL, buffer, NULL, &err);
+    Dart_Isolate isolate = Dart_CreateIsolate(NULL, NULL, buffer, NULL, &err);
     if (isolate == NULL) {
       OS::Print("Creation of isolate failed '%s'\n", err);
       free(err);
     }
     EXPECT(isolate != NULL);
     return isolate;
   }
 
   RunEntry* const run_;
 };
@@ skipping 102 matching lines @@
     } else {                                                                   \
       dart::Expect(__FILE__, __LINE__).Fail(                                   \
           "expected '%s' to be an error handle but found a valid handle.\n",   \
           #handle);                                                            \
     }                                                                          \
   } while (0)
 
 }  // namespace dart
 
 #endif  // VM_UNIT_TEST_H_