Things in components should live in namespaces that match their
component. Unfortunately "sync" is a symbol defined in the std library,
so in this case we are using "syncer".

This CL does the following things inside //components/sync:

- Replaces all uses of syncer_v2, sync_driver, sync_driver_v2, and
  browser_sync with syncer.
- Adds syncer namespace to some classes that were missing a namespace.
- Removes almost all "syncer::" prefixes since they became redundant.

Everything outside the component is just fixing namespace prefixes and forward
 declarations. I also fixed *some* lints, especially in headers outside of the
 component.

This script was the starting point for this CL: http://pastebin.com/PPhPTtRK

This CL was previously reverted due to a strange leak resulting from a
redefinition of Syncer in the ui_model_worker_unittest.cc file.

BUG=646685
TBR=brettw,skym,caitkp

Review-Url: https://codereview.chromium.org/2388163002
Cr-Commit-Position: refs/heads/master@{#422494}