When creating, updating or deleting draft comments, the diff containing
the draft does not need to be kept open for the underlying requests to
succeed. However, in a number of ways, the draft UI suggests that it
does. This results in the draft writing process feeling like a blocking
experience when it need not be.
Change the draft UI to feel less blocking:
- Instead of merely disabling the textarea when saving, the textarea is
hidden and the presentation form of the message is shown immediately.
- Instead of disabling a draft as its being discarded, the draft
disappears immediately.
- The `_savingMessage` is removed.
Bug: Issue 6970
Change-Id: Ia396f0f1780571def84be0d20f19c98bdb0b0cde
8635c8effb