Allow debuggerd read access to shared_relro files.

Addresses the following denial when debuggerd attempts to stat Webview mmap'd
shared relro files on process crash.  Full read permissions may not be necessary:

W/debuggerd(  185): type=1400 audit(0.0:97): avc: denied { search } for name="shared_relro" dev="mmcblk0p28" ino=618955 scontext=u:r:debuggerd:s0 tcontext=u:object_r:shared_relro_file:s0 tclass=dir

Bug: 17101854
Change-Id: I11eea85668ba033c554e5aab99b70a454fb75164