When IME is no longer shown, notify IMS to hide the window surface.
This reclaims the memory allocated to IME window surface.
Fix: 150163310
Test: atest CtsInputMethodTests
Manually:
1. Open any app that has editor and run
adb shell dumpsys SurfaceFlinger | grep Total
2. Note down total memory
3. Tap on editor and IME shows. Note down memory
using command in #1. It should go up by ~27MB
4. Hide IME and note down memory again.
It should revert to original value in #1.
Change-Id: I6c2a13dd40b22d3fd62b4763ba369992e5ff1138
94c9a8328e