Race condition in Toast.

1. mTN.mNextView set in toast.show() but can be invalided by posted
runnable mTN.mHide. If application call toast.cancel() right before
toast.show(), this problem happen.

2. mTN.hide() is called twice if toast.cancel() is called.

Conflicts:

	core/java/android/widget/Toast.java

Change-Id: I554c5d44c59e18f5066f6175faec3e256b4e40d6