Soundcloud widgets not blocked on tumblr pop-out

**WHAT ACTUALLY HAPPENED**
1. Load tumblr dashboard, queue or drafts.
2. Hover over the name of a blog which has posted soundcloud posts.
3. Click the pop-up such that the blog slides out from the right side of the window.
4. Soundcloud widgets in the dynamically loaded slide-out are not blocked.

**WHAT I EXPECT TO HAPPEN**

Soundcloud widgets should be blocked at all times.

Reproduce the Tumblr dashboard flow through queue or drafts, then open a blog's slide-out and inspect the dynamically loaded SoundCloud widgets. Search the JavaScript extension code for SoundCloud blocking and handling of dynamically inserted content; done means those widgets are blocked in the slide-out as well as the initially loaded page.

Written by the indexing model from the issue text.