Sluggish tab performance in UI

[barryoneill]

Question/Issue Overview

The HTML tab can sometimes take a significant time to render, especially when the attachments are in place.

Expected Behavior

Even with a few small attachments, render of the HTML tab should be almost instantaneous locally.

Reproducible Sequence

1. Use the script send-sample-emails.py to add some data to a local holdmail install.
2. In chrome, open any of the mails that it added (they all embed an image)
3. See that there is a delay rendering the HTML tab that contains an image.

Additional Information

• Although this is reproducible with attachments, I'm not sure the size of the attachments are to blame. * It could be related to what appears to be all tabs loading their contents immediately, even though only one is open.
• Looking at the performance tab, there's a 2 second rendering pause, even though that PNG is <70kb (see attachment)
• Could it be the 'Original Content' tab? That renders the whole Base64 decoded value for the image. If you open an email that also has an attachment (not just the embedded image), this rendering block does seem to take longer.
• Maybe we could try rendering the tabs only on display?