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
Merge "Race condition in Toast." into jb42