sync: Route local sessions events to SessionsSyncManager

Builds on https://codereview.chromium.org/74653002/

What's left after this:
- Full reassociation on ProcessSyncChanges errors.
- Integration Tests
- Stale Session pruning.

Since GetActiveEntry is now deprecated, switched to use GetVisibleEntry instead per bug 273710.

BUG=98892
R=rlarocque@chromium.org, zea@chromium.org

Review URL: https://codereview.chromium.org/79973002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238317 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238317
Simplify fileBrowserPrivate.getDriveConnectionStatus().

The "reasons" field had been a subset of {NO_SERVICE, NO_NETWORK, NOT_READY},
but it is now used only for signaling errors when it has NOT_READY
without other reasons. This can more simply be represented
by a single "reason" field whose value is set in the order:
NO_SERVICE > NO_NETWORK > NOT_READY, i.e., NOT_READY is set
only when other two states are not set.

BUG=237427
R=benwells@chromium.org, yoshiki@chromium.org

Review URL: https://codereview.chromium.org/98493003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238318 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238318