Exclude system decor area from tap detection.

If we have system decor (status bar/ navigation bar), we want to
exclude that from the tap detection. Otherwise, if the app is partially
placed under some system button (eg. Recents, Home), pressing that
button would cause a full series of unwanted transfer focus/resume/pause,
before we could go home.

Change-Id: Idd408bd69f5064f906bb9f8e2b2385c26a6a6929