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

runtime/bin/dartutils.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 BIN_DARTUTILS_H_
 #define BIN_DARTUTILS_H_
 
 #include "bin/builtin.h"
 #include "bin/utils.h"
 #include "include/dart_api.h"
@@ skipping 67 matching lines @@
   static bool IsDartUriLibURL(const char* url_name);
   static bool IsDartUtfLibURL(const char* url_name);
   static Dart_Handle CanonicalizeURL(CommandLineOptions* url_mapping,
                                      Dart_Handle library,
                                      const char* url_str);
   static Dart_Handle ReadStringFromFile(const char* filename);
   static Dart_Handle LoadSource(CommandLineOptions* url_mapping,
                                 Dart_Handle library,
                                 Dart_Handle url,
                                 Dart_LibraryTag tag,
-                                const char* filename,
-                                Dart_Handle import_map);
+                                const char* filename);
   static bool PostNull(Dart_Port port_id);
   static bool PostInt32(Dart_Port port_id, int32_t value);
 
   // Create a new Dart OSError object with the current OS error.
   static Dart_Handle NewDartOSError();
   // Create a new Dart OSError object with the provided OS error.
   static Dart_Handle NewDartOSError(OSError* os_error);
 
   static const char* kDartScheme;
   static const char* kDartExtensionScheme;
@@ skipping 190 matching lines @@
 
 class CObjectUint8Array : public CObject {
  public:
   DECLARE_COBJECT_CONSTRUCTORS(Uint8Array)
 
   int Length() const { return cobject_->value.as_byte_array.length; }
   uint8_t* Buffer() const { return cobject_->value.as_byte_array.values; }
 };
 
 #endif  // BIN_DARTUTILS_H_