Fix TextUtils#commaEllipsize

Bug 3400770

TextUtils#commaEllipsize creates a MeasuredText "mt" object with the
text to be ellipsized. It calls setPara which initializes mt's mPos
member to be 0. It then calls addStyleRun which moves mPos to the end
of the string. The loop back in commaEllipsize then calls mt addStyleRun
again and this causes IndexOutOfBoundsException, because the paint
object is trying to measure text past the text's length.

It seems this was a typo and that the tempMt variable should be used,
because the code is trying to measure the format string...not the
the string to be ellipsized. This makes the saner parts of CTS test
for this method pass now.

Change-Id: Ib6aa6e4bbd6afff4c95ad4c4d51a384cc1389875