The position of IME is wrong (HiDPI)

Steps to reproduce:
1. use simplebrowser demo open https://docs.google.com/document/d/1D2YoMcbhp4z2uWG9sJAysgpMmXyQYzpdZ56l8KXvYZk/edit
2. try typing some words into URL bar.
3. then typing some words into google docs, the position of IME was wrong.

I guess that because the position of the IME does not update when the cursor focus in webpage. The qt 5.7.1 work fine.