Inject automatically on install etc., add mime types, and fix nits.

Remove the installation notes page, and instead inject the content script
automatically when the extension is installed, updated, or re-enabled.
Likewise, disable it (remove the keyboard listener) when the extension is
uninstalled or disabled.

Also fix a punctuation nit, and add PDF and chat mime types to the list of
recognized embedded applets.

BUG=639645, 645517

Review URL: .
9 files changed
tree: 24b13034e41827c58273965f1fea7790790bac57
  1. go-back-with-backspace/
  2. .gitignore