Widen permissions on synthesized files.

When synthesized files are written to app private data dirs,
they are written with owner/grp set to the TTS engine and
are inaccessible by the app itself. This is a reported regression
from gingerbread behaviour. Note that the dir in which the
engine writes files is itself already world writable.

bug:5523587
Change-Id: I2cb26c6f3c3d9cb3cedd60fab32c99a85a27f4b1