Worker: Rename worker components to clarify what they work for (part 2)

This CL renames WorkerObjectProxy to InProcessWorkerObjectProxy because
WorkerObjectProxy works only for in-process workers (DedicatedWorker and
CompositorWorker). In addition, this removes unnecessary header inclusions.

Part 1: https://codereview.chromium.org/1888703002/

BUG=603785

Review URL: https://codereview.chromium.org/1897193002

Cr-Commit-Position: refs/heads/master@{#388194}
16 files changed