Prune archives uploaded to google storage.

BUG=

Review URL: https://codereview.chromium.org/1687843002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/build@298702 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/scripts/slave/zip_build.py b/scripts/slave/zip_build.py
index 98039e0..a756ba4 100755
--- a/scripts/slave/zip_build.py
+++ b/scripts/slave/zip_build.py
@@ -350,7 +350,11 @@
   zip_base, zip_ext, versioned_file = MakeVersionedArchive(
       zip_file, version_suffix, options)
 
-  PruneOldArchives(staging_dir, zip_base, zip_ext, prune_limit=10)
+  prune_limit = 10
+  if options.build_url.startswith('gs://'):
+    # Don't keep builds lying around when uploading them to google storage.
+    prune_limit = 3
+  PruneOldArchives(staging_dir, zip_base, zip_ext, prune_limit=prune_limit)
 
   # Update the latest revision file in the staging directory
   # to allow testers to figure out the latest packaged revision