Improve the heuristics for "pub get" is needed.

test/test_pub.dart

 // Copyright (c) 2013, 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.
 
 /// Test infrastructure for testing pub.
 ///
 /// Unlike typical unit tests, most pub tests are integration tests that stage
 /// some stuff on the file system, run pub, and then validate the results. This
 /// library provides an API to build tests like that.
 library test_pub;
@@ skipping 696 matching lines @@
 ///
 /// [sandbox] is a list of path dependencies to be found in the sandbox
 /// directory. [pkg] is a list of packages in the Dart repo's "pkg" directory;
 /// each package listed here and all its dependencies will be linked to the
 /// version in the Dart repo.
 ///
 /// [hosted] is a list of package names to version strings for dependencies on
 /// hosted packages.
 void createLockFile(String package, {Iterable<String> sandbox,
     Iterable<String> pkg, Map<String, String> hosted}) {
-  var cache = new SystemCache.withSources(
-      rootDir: p.join(sandboxDir, cachePath));
+  schedule(() async {
+    var cache = new SystemCache.withSources(
+        rootDir: p.join(sandboxDir, cachePath));
 
-  var lockFile = _createLockFile(cache.sources,
-      sandbox: sandbox, pkg: pkg, hosted: hosted);
+    var lockFile = _createLockFile(cache.sources,
+        sandbox: sandbox, pkg: pkg, hosted: hosted);
 
-  d.dir(package, [
-    d.file('pubspec.lock', lockFile.serialize(null)),
-    d.file('.packages', lockFile.packagesFile(package))
-  ]).create();
+    await d.dir(package, [
+      d.file('pubspec.lock', lockFile.serialize(null)),
+      d.file('.packages', lockFile.packagesFile(package))
+    ]).create();
+  }, "creating lockfile for $package");
+}
+
+/// Like [createLockFile], but creates only a `.packages` file without a
+/// lockfile.
+void createPackagesFile(String package, {Iterable<String> sandbox,
+    Iterable<String> pkg, Map<String, String> hosted}) {
+  schedule(() async {
+    var cache = new SystemCache.withSources(
+        rootDir: p.join(sandboxDir, cachePath));
+
+    var lockFile = _createLockFile(cache.sources,
+        sandbox: sandbox, pkg: pkg, hosted: hosted);
+
+    await d.dir(package, [
+      d.file('.packages', lockFile.packagesFile(package))
+    ]).create();
+  }, "creating .packages for $package");
 }
 
 /// Creates a lock file for [package] without running `pub get`.
 ///
 /// [sandbox] is a list of path dependencies to be found in the sandbox
 /// directory. [pkg] is a list of packages in the Dart repo's "pkg" directory;
 /// each package listed here and all its dependencies will be linked to the
 /// version in the Dart repo.
 ///
 /// [hosted] is a list of package names to version strings for dependencies on
@@ skipping 264 matching lines @@
         _lastMatcher.matches(item.last, matchState);
   }
 
   Description describe(Description description) {
     return description.addAll("(", ", ", ")", [_firstMatcher, _lastMatcher]);
   }
 }
 
 /// A [StreamMatcher] that matches multiple lines of output.
 StreamMatcher emitsLines(String output) => inOrder(output.split("\n"));