Fix for bug: Gmail (and other places): cursor placed on top of letter

This patch fixes bug 7346656. In this particular case, the text line in
the EditText was split into multiple spans, with the boundary between
the "r" and "," in "r,". These were being drawn as two separate runs,
but measured as a single run, leading to inconsistent measurements
because this is a kern pair in Roboto.

The fix is to eliminate the special-case code for measuring. This will
actually improve efficiency, as the value computed in one pass is now
more likely to be reused in another.

Change-Id: I04142a0ec98f280fc1027c7cbdbf903e3096f8e4