Decouple PolicyManager native initialization and registration with activities.
When Switching between Document mode and single activity mode. A new
ChromiumApplication is created that does not have the PolicyManager yet.
This caused a NPE which was fixed by adding a statically initialized list that
was never used as List#remove does not complain for non-existent values.
By decoupling native and java initializations of PolicyManager. We can do the same thing with stronger asserts in place.
BUG=490894
Review URL: https://codereview.chromium.org/
1149353004
Cr-Commit-Position: refs/heads/master@{#331137}