1. The crash was happening if: two active pointers are performing a drag;
there are some inactive pointers down; the main dragging pointer (we are
merging the dragging pointers into one) goes up; now an inactive pointer
goes up and the explorer tries to inject up for the dragging pointer
which is no longer in the event resulting in a crash. Basically two
problems: inactive pointers were not ignored; 2) having only one
active pointer should not only send the up event but also transition
the explorer in touch exploring state.
bug:6874128
Change-Id: I341fc360ebc074fe3919d5ba3b98ee5cb08dd71e
03e7b88815