Do not show selection action mode when the TextView is not shown.

OnPreDraw is called even if the View is not visible.
So need to check isShown() and hasWindowFocus() before calling
starting selection action mode.

This hack is originally introduced for keeping selection on device rotation.
I manually verified this issue does not revive with this CL.

Bug: 22036870
Change-Id: I814db6165e2345fcacedcbd399c1a3985501c8fd