Fix bug in measurement of paragraphs

This fixes b/16510772.

When measuring paragraphs, leading margins should be taken into account.
When computing line width, the margin should be added to the absolute
value of the extent (there were missing parenthesis). Both of these
caused views with leading margins to be rendered incorrectly.

Change-Id: I5029b2790a249192a858eb226d7b793d0622a70d