Disable actions in the Files view menu that are not allowed for pub cache projects.

R=danrubel@google.com
BUG=

Review URL: https://codereview.chromium.org//654773003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41219 260f80e4-7a28-3924-810f-c04153c831b5