Reduce the frequency of dirty calculations in inlineEditor.

inlineEditor no longer calculates the dirty state on every single key
press. Instead, it calculates it at most once every 200ms. This helps to
improve performance when the text field is large.

When it does calculate, the default behavior is now to first compare the
lengths of the strings. If those differ, then there's no need to compare
the string contents.

Reviewed at https://reviews.reviewboard.org/r/6426/