Added tavern support to Spark.

Added tavern support to Spark.

Now when a pubspec.yaml file is selected inside a chrome app project
(i.e. a directory which has a manifest.json file) then hitting the run
button will download the selected dependencies.

The tavern log output should also appear in a separate window.

R=tapted@chromium.org

Committed: https://github.com/tapted/bleeding_edge/commit/9600ba5

[pajamallama, 2014-01-24 04:00:31]

Spark support nom nom nom.

[tapted, 2014-01-24 06:14:34]

crap. stupid rietveld. The base files are missing - can you re-upload?

[tapted, 2014-01-24 06:31:51]

Actually looking at the diff in email (and variable width font :o), I think you
just need to fix quote in
+    if (resource.name == "pubspec.yaml") {

to be single quotes. So lgtm.

[pajamallama, 2014-01-28 00:01:12]

Committed patchset #2 manually as r9600ba5 (presubmit successful).