Bug 984328 - [Keyboard][V1.3T] The alternative char menu cannot be
displayed
 - To set initial value of cached window height/width when the keyboard
   is relaunched after memory pressure.
Merge pull request #17737 from RudyLu/keyboard/Bug984328_master

Bug 984328 - [Keyboard][V1.3T] The alternative char menu cannot be
r=timdream