Steps to Reproduce

1. TextField(maxLength: 5) (Value can be any integer greater than zero).
2. Using a keyboard with composing, such as the Chinese keyboard.
3. Input until the characters length more than the max length, and keep composing status.
4. At this time the characters might flashing, if this appears, press delete button.
5. The app crashed.

Environment

Platform: iOS
Flutter version: 1.0.0~master