Give WebViewZygote process shared app GID.

So WebViewZygote can access profiles belonging to the app.

Bug: 254422654
Flag: EXEMPT bugfix
Test: inspect /proc/pid/maps to verify profiles are loaded
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:4e2db7cea643a55aa7d0b10659334c26bfc9a571)
Merged-In: I33ebb8c2f8115cd3f25099987dfb5dad38ed057c
Change-Id: I33ebb8c2f8115cd3f25099987dfb5dad38ed057c