RELAND: InMemory MediaCapabilities DB for Guest/Incognito

Original CL was reverted:

Reland now possible thanks to:

Prior to this change, Guest mode has an empty read-only DB and Incongito
has a read-only DB. This CL allows both profiles to write to an "in
memory" database that disapears when the profile is destroyed.

This improves the experience for the user and avoids the possibility
of using MediaCapabilites to detect incognito/guest profiles.

Bug: 796280, 855631, 855215
Change-Id: Ideb9dd2eabab2e594a24dd9b514557e473c3afc0
Commit-Queue: Mounir Lamouri <>
Reviewed-by: Scott Violet <>
Reviewed-by: Mounir Lamouri <>
Reviewed-by: John Abd-El-Malek <>
Cr-Commit-Position: refs/heads/master@{#574633}
17 files changed