As part of the MD settings redesign, bettes@ and I would like to revise several empty state messages to improve the tone (remove snarkiness) and provide helpful info for the user. 

1. Extensions (IDS_EXTENSIONS_NONE_INSTALLED)
Current: "Boo... You have no extensions :-("
Proposed: "Find extensions and themes on the <link>Chrome Web Store</link>"

Link is https://chrome.google.com/webstore/category/extensions

2. Downloads (IDS_MD_DOWNLOAD_NO_DOWNLOADS)
Current: "Nothing to see here"
Proposed: "Files you download appear here"

3. History (IDS_HISTORY_NO_RESULTS)
Current: No history entries
Proposed: "Your browsing history appears here"

4. Bookmarks
Current: "This folder is empty" OR "No bookmarks here" (not clear which is currently in use)
Proposed: "To bookmark pages, click the star in the address bar"