[Sync] Fix namespaces for the sync_sessions component.

Things within a component should have a namespace that matches its name.

BUG=646685
TBR=jam

Review-Url: https://codereview.chromium.org/2343463003
Cr-Commit-Position: refs/heads/master@{#418878}
94 files changed