Add support for importing using "package:" to the standalone VM.

runtime/bin/builtin.dart

 // 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.
 
 #library("builtin");
 
 void print(arg) {
   _Logger._printString(arg.toString());
 }
 
 void exit(int status) {
   if (status is !int) {
     throw new IllegalArgumentException("int status expected");
   }
   _exit(status);
 }
 
 _exit(int status) native "Exit";
 
 class _Logger {
   static void _printString(String s) native "Logger_PrintString";
 }
 
 
 // Code to deal with URI resolution for the standalone binary.
 // For Windows we need to massage the paths a bit according to
 // http://blogs.msdn.com/b/ie/archive/2006/12/06/file-uris-in-windows.aspx
 var _is_windows;
 
+// The URI that the entrypoint script was loaded from. Remembered so that
+// package imports can be resolved relative to it.
+Uri _entrypoint;
+
 void _logResolution(String msg) {
   final enabled = false;
   if (enabled) {
     _Logger._printString(msg);
   }
 }
 
 String _resolveScriptUri(String cwd, String scriptName, bool windows) {
   _is_windows = windows;
   _logResolution("# Current working directory: $cwd");
   _logResolution("# ScriptName: $scriptName");
   if (windows) {
     // Convert
     // C:\one\two\three
     // to
     // /C:/one/two/three
     cwd = "/${cwd.replaceAll('\\', '/')}";
     _logResolution("## cwd: $cwd");
     if ((scriptName.length > 2) && (scriptName[1] == ":")) {
       // This is an absolute path.
       scriptName = "/${scriptName.replaceAll('\\', '/')}";
     } else {
       scriptName = scriptName.replaceAll('\\', '/');
     }
     _logResolution("## scriptName: $scriptName");
   }
   var base = new Uri(scheme: "file", path: cwd.endsWith("/") ? cwd : "$cwd/");
-  var resolved = base.resolve(scriptName);
-  _logResolution("# Resolved to: $resolved");
-  return resolved.toString();
+  _entrypoint = base.resolve(scriptName);
+  _logResolution("# Resolved script to: $_entrypoint");
+
+  return _entrypoint.toString();
 }
 
 String _resolveUri(String base, String userString) {
   var baseUri = new Uri.fromString(base);
   _logResolution("# Resolving: $userString from $base");
   var resolved = baseUri.resolve(userString);
   _logResolution("# Resolved to: $resolved");
   return resolved.toString();
 }
 
 String _resolveExtensionUri(String base, String userString) {
   var uri = new Uri.fromString(userString);
   if ("dart-ext" != uri.scheme) {
     throw "Not a Dart extension uri: $uri";
   }
   var schemelessUri = new Uri(path: uri.path);
   var baseUri = new Uri.fromString(base);
   _logResolution("# Resolving: $userString from $base");
   var resolved = baseUri.resolveUri(schemelessUri);
   resolved = new Uri(scheme: 'dart-ext', path: resolved.path);
   _logResolution("# Resolved to: $resolved");
   return resolved.toString();
 }
 
 String _filePathFromUri(String userUri) {
   var uri = new Uri.fromString(userUri);
   _logResolution("# Getting file path from: $uri");
-  if ("file" != uri.scheme) {
-    // Only handling file URIs in standalone binary.
-    _logResolution("# Not a file URI.");
-    throw "Not a file uri: $uri";
+
+  switch (uri.scheme) {
+  case 'file':    return _filePathFromFileUri(uri);
+  case 'package': return _filePathFromPackageUri(uri);
+
+  default:
+    // Only handling file and package URIs in standalone binary.
+    _logResolution("# Not a file or package URI.");
+    throw "Not a known scheme: $uri";
   }
+}
+
+String _filePathFromFileUri(Uri uri) {
   var path = uri.path;
   _logResolution("# Path: $path");
   if (_is_windows) {
     // Drop the leading / before the drive letter.
     path = path.substring(1);
     _logResolution("# path: $path");
   }
   return path;
 }
+
+String _filePathFromPackageUri(Uri uri) {
+  // Get the path to the package directory.
+  var baseDir = _entrypoint.path;
+
+  // Remove any extension.
+  var lastDot = baseDir.lastIndexOf(".");
+  if (lastDot != -1) {
+    baseDir = baseDir.substring(0, lastDot);
+  }
+
+  var path = "$baseDir.packages/${uri.path}";
+  _logResolution("# Package: $path");
+  return path;
+}