Split EmbeddedWorkerDevToolsManager into two for Shared- and ServiceWorker

      One more follow-up patch for
https://codereview.chromium.org/761923004/#msg18
https://codereview.chromium.org/814513003/

- Split EmbeddedWorkerDevToolsManager into two, Shared- and ServiceWorkerDevToolsManager, and made them inherit from EmbeddedWorkerDevToolsManager
- Renamed EmbeddedWorkerDevToolsAgentHost to WorkerDevToolsAgentHost
- Renamed EmbeddedWorkerDevToolsManager to WorkerDevToolsManager

BUG=443470
TEST=SharedWorkerDevToolsMangerTest\*

Review URL: https://codereview.chromium.org/817653002

Cr-Commit-Position: refs/heads/master@{#309412}