Support reloading from source on top of a script snapshot.

runtime/include/dart_api.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 RUNTIME_INCLUDE_DART_API_H_
 #define RUNTIME_INCLUDE_DART_API_H_
 
 /** \mainpage Dart Embedding API Reference
@@ skipping 2688 matching lines @@
  *
  * This tag indicates that the embedder should canonicalize 'url' with
  * respect to 'library'.  For most embedders, the
  * Dart_DefaultCanonicalizeUrl function is a sufficient implementation
  * of this tag.  The return value should be a string holding the
  * canonicalized url.
  *
  * Dart_kScriptTag
  *
  * This tag indicates that the root script should be loaded from
- * 'url'.  The 'library' parameter will always be null.  Once the root
+ * 'url'.  If the 'library' parameter is not null, it is the url of the
+ * package map that should be used when loading.  Once the root
  * script is loaded, the embedder should call Dart_LoadScript to
  * install the root script in the VM.  The return value should be an
  * error or null.
  *
  * Dart_kSourceTag
  *
  * This tag is used to load a file referenced by Dart language "part
  * of" directive.  Once the file's source is loaded, the embedder
  * should call Dart_LoadSource to provide the file contents to the VM.
  * The return value should be an error or null.
  *
  * Dart_kImportTag
  *
  * This tag is used to load a script referenced by Dart language
  * "import" directive.  Once the script is loaded, the embedder should
  * call Dart_LoadLibrary to provide the script source to the VM.  The
  * return value should be an error or null.
  */
-typedef Dart_Handle (*Dart_LibraryTagHandler)(Dart_LibraryTag tag,
-                                              Dart_Handle library,
-                                              Dart_Handle url);
+typedef Dart_Handle (*Dart_LibraryTagHandler)(
+    Dart_LibraryTag tag,
+    Dart_Handle library_or_package_map_url,
+    Dart_Handle url);
 
 /**
  * Sets library tag handler for the current isolate. This handler is
  * used to handle the various tags encountered while loading libraries
  * or scripts in the isolate.
  *
  * \param handler Handler code to be used for handling the various tags
  *   encountered while loading libraries or scripts in the isolate.
  *
  * \return If no error occurs, the handler is set for the isolate.
@@ skipping 459 matching lines @@
 
 
 /**
  *  Returns whether the VM only supports running from precompiled snapshots and
  *  not from any other kind of snapshot or from source (that is, the VM was
  *  compiled with DART_PRECOMPILED_RUNTIME).
  */
 DART_EXPORT bool Dart_IsPrecompiledRuntime();
 
 #endif /* INCLUDE_DART_API_H_ */ /* NOLINT */