Add KeepaliveImpulse to extension process manager.

Impulses are an efficient way to handle certain types
of activity from extensions. E.g. the work in progress
to keep NaCl plugins in background pages alive. An
Increment / Decrement approach would require extensive
and fragile instrumentation of all APIs. Impulses
can be sent upon any api activity and act as an
implicit increment with a timed out decrement.

See design doc:
https://docs.google.com/a/chromium.org/document/d/1mI0lS1rfAf-BAGLmWAEcWy37Xq9dOvgfMx8OqeUMXts/edit#

BUG=298339

Review URL: https://codereview.chromium.org/60613004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238261 0039d316-1c4b-4281-b951-d872f2087c98
kiosk: Show enrollment screen first if needed.

- Show enrollment screen by default after OOBE if the device is set
  to auto enrollment and is not yet enrolled;
- Update screen loading code to defer Initialize() call for async
  loaded screen until the assets are loaded;

BUG=322666
TEST=LoginUITest.ShowEnrollmentFirst

Review URL: https://codereview.chromium.org/83293004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238262 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238262
Dispatch FileStatus change events for LocalToRemote sync too

BUG=240165
TEST=manual
R=nhiroki@chromium.org, tzik@chromium.org

Review URL: https://codereview.chromium.org/98803002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238263 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238263