Messages with images or media were causing the scroll position to jump
around when they loaded, because rendering them changed the height of their
elements from 0 to full-height sometime after they were inserted into
the DOM.
Now when rendering attachments, we wait for them to load so they can
render at full height immediately, then warn our parent message list
before and after a potential height change, so the scroll position can
be saved and reset.
// FREEBIE
Bind the sub-view to some data when we initialize it, rather than
passing it in on render. That means the image view click handler will
only ever open the blob we bound it to, even if its src attr changes for
some reason, which should never happen, but if it does, it's nice to
guard against opening arbitrary urls found in the dom.
// FREEBIE
Images that are attached to messages, either sent or received
can be opened in a new tab by clicking on them.
The previous approach that used Anchors to open the image
attachmets failed in various systems because:
- Chrome on Windows recognised "blob" as protocol and tried
to find an app for it
- Chromium on Ubuntu didn't open a new window to load the URL
The new approach adds a "click" listener to the IMG element and
opens the link using window.open (which seems to be working globaly).
Resolves: #252
Converting attachment data to base64-encoded data uris takes O(n) and
there's no need! URL.createObjectURL returns a magic link that can be
set as the `src` attribute to `img`, `video`, and `audio` tags to load
blob data directly without copying.
https://developer.mozilla.org/en-US/docs/Web/API/URL/createObjectURL
