Change permissions on ref profile so that ART can read it

The reference profile is now used to determined whether or not
ART should trigger a profile save earlier.

Test: manual
adb shell stop;
adb shell setprop dalvik.vm.ps-min-first-save-ms 300;
adb shell setprop dalvik.vm.extra-opts -verbose:profiler;
adb shell start;

Bug: 185979271
Change-Id: I49002965e27e41b2beb753335962edbd93c54146