Trim whitespace from parsed filename in Android v21.

Trim whitespace from parsed filename in Android v21.

The entire text content of the 'font' element is currently used as the
file name. This wasn't an issue in earlier versions, as the 'file'
element was dedicated to only containing the file name. The new 'font'
element also contains a number of attributes and potentially other tags.
This means that a 'font' element can become quite long, making it
desireable to be able to split it across multiple lines.

However, splitting the 'font' element across multiple lines is currently
difficult and awkward as any whitespace outside of tags will be
considered part of the file name. This change means that any leading or
trailing whitespace will not be considered part of the file name.

This only applies to v21 and later files, so while this restricts font
file names from beginning and ending with whitespace, it is unlikely to
break any users in practice. It is probably also undesireable to have
font files with names that begin or end with whitespace in any event.

Review URL: https://codereview.chromium.org/1125413003