message: Support Undo also on Composition and Conversion state with a PK
  Startblock:
  cl/496316291 is submitted
diff: @@ -63,7 +63,7 @@ Composition VirtualRight MoveCursorRight
  Composition VirtualEnter Commit
  Conversion Backspace Cancel
  Conversion Ctrl a SegmentFocusFirst
  -Conversion Ctrl Backspace Cancel
  +Conversion Ctrl Backspace Undo
  Conversion Ctrl d SegmentFocusRight
  Conversion Ctrl Down CommitOnlyFirstSegment
  Conversion Ctrl e ConvertPrev
  