IMEContentObserver notifies IME of 3 notifications at most when editor is changed.
The order is:
1. text change (with merged range if 2 or more change occurred during an edit transaction)
2. selection change (only the latest selection change. other changes occurred before that during an editor transaction are ignored)
3. position change (scrolled, resized, window moved, etc)
This does not check the behavior in designMode because some operation in testWithHTMLEditor() causes unexpected behavior, e.g., moving focus. It *might* be bug of design mode. However, it doesn't matter for this bug. The important thing of this bug is, there should be automated tests for IMEContentObserver. And fortunately, IMEContentObserver does not check the type of editor. So, it's enough to test only contenteditable element for HTMLEditor at least for now. Therefore, I gave up to test it in designMode for now.
MozReview-Commit-ID: 7L6ZlbVMU2P
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extra : rebase_source : 8282fe7aa2f4d405f2576f05d46b60b044223855
