Fix JNI reference leak in NativeActivity. (DO NOT MERGE)

This change ensures that the native activity releases the KeyEvent
objects that it allocates since they will not be released
automatically and eventually the JNI slot table will overflow
and crash the process.

Bug: 3170494
Change-Id: I2ea527f056096fae9bc9e7685dccb56ec7a0e8b4
1 file changed