Use environment variables to find the Dart SDK and the Pub cache directory.

utils/pub/io.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.
 
 /**
  * Helper functionality to make working with IO easier.
  */
 #library('io');
 
 #import('dart:io');
@@ skipping 315 matching lines @@
 /**
  * Spawns and runs the process located at [executable], passing in [args].
  * Returns a [Future] that will complete the results of the process after it
  * has ended.
  *
  * If [pipeStdout] and/or [pipeStderr] are set, all output from the subprocess's
  * output streams are sent to the parent process's output streams. Output from
  * piped streams won't be available in the result object.
  */
 Future<PubProcessResult> runProcess(String executable, List<String> args,
-    [workingDir, bool pipeStdout = false, bool pipeStderr = false]) {
+    [workingDir, Map<String, String> environment, bool pipeStdout = false,
+    bool pipeStderr = false]) {
   int exitCode;
 
   final options = new ProcessOptions();
   if (workingDir != null) {
     options.workingDirectory = _getDirectory(workingDir).path;
   }
+  options.environment = environment;
 
   final process = Process.start(executable, args, options);
 
   final outStream = new StringInputStream(process.stdout);
   final processStdout = <String>[];
 
   final errStream = new StringInputStream(process.stderr);
   final processStderr = <String>[];
 
   final completer = new Completer<PubProcessResult>();
@@ skipping 116 matching lines @@
   return new Directory(entry);
 }
 
 /**
  * Gets a [Uri] for [uri], which can either already be one, or be a [String].
  */
 Uri _getUri(uri) {
   if (uri is Uri) return uri;
   return new Uri.fromString(uri);
 }