Clear calling identity when binding a11y services

When a UiAutomation is destroyed, accessibility services may get
enabled as a side effect. That was causing these services to be
enabled in a binder thread, which threw a SecurityException.

Bug: 28268310
Bug: 28163652
Change-Id: Ie25ab05569b5b21b5f30e7d7eed24ef73b7ba159
1 file changed