Teach dart_package to understand the packages/ subdirectory

mojo/dart/apptest/pubspec.lock

Index: mojo/dart/apptest/pubspec.lock
diff --git a/mojo/dart/apptest/pubspec.lock b/mojo/dart/apptest/pubspec.lock
new file mode 100644
index 0000000000000000000000000000000000000000..d9eec107a0f8fb334d8c10bee328eb5cf93e19de
--- /dev/null
+++ b/mojo/dart/apptest/pubspec.lock
@@ -0,0 +1,19 @@
+# Generated by pub

[tonyg, 2015/04/08 13:52:37]

It seems worth documenting the process of updating the locked versions in a
README.md somewhere. Is it something like, rm this file, manually pub get, then
check in the new one? Or is there a better way?

[blundell, 2015/04/09 11:53:41]

You update pubspec.yaml and then run "pub upgrade". Do you see a good place to
document this?

[tonyg, 2015/04/09 12:55:56]

One idea for a follow-up patch would be to output warnings with instructions
when newer packages are available. Then everyone running gclient sync would know
it is time to attempt a roll.

+# See http://pub.dartlang.org/doc/glossary.html#lockfile
+packages:
+  matcher:
+    description: matcher
+    source: hosted
+    version: "0.11.4+4"
+  path:
+    description: path
+    source: hosted
+    version: "1.3.4"
+  stack_trace:
+    description: stack_trace
+    source: hosted
+    version: "1.2.4"
+  unittest:
+    description: unittest
+    source: hosted
+    version: "0.11.5+4"