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

runtime/vm/raw_object.h

 // 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.
 
 #ifndef VM_RAW_OBJECT_H_
 #define VM_RAW_OBJECT_H_
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/token.h"
@@ skipping 630 matching lines @@
 
   RAW_HEAP_OBJECT_IMPLEMENTATION(Library);
 
   RawObject** from() { return reinterpret_cast<RawObject**>(&ptr()->name_); }
   RawString* name_;
   RawString* url_;
   RawScript* script_;
   RawString* private_key_;
   RawArray* dictionary_;         // Top-level names in this library.
   RawArray* anonymous_classes_;  // Classes containing top-level elements.
-  RawArray* import_map_;         // Map of import variable names to strings.
   RawArray* imports_;            // List of libraries imported without prefix.
   RawArray* imported_into_;      // List of libraries where this library
                                  // is imported into without a prefix.
   RawLibrary* next_registered_;  // Linked list of registered libraries.
   RawArray* loaded_scripts_;     // Array of scripts loaded in this library.
   RawObject** to() {
     return reinterpret_cast<RawObject**>(&ptr()->next_registered_);
   }
 
   intptr_t num_imports_;         // Number of entries in imports_.
@@ skipping 695 matching lines @@
   intptr_t type_;  // Uninitialized, simple or complex.
   intptr_t flags_;  // Represents global/local, case insensitive, multiline.
 
   // Variable length data follows here.
   uint8_t data_[0];
 };
 
 }  // namespace dart
 
 #endif  // VM_RAW_OBJECT_H_