Remove Inspector related methods from WebServiceWorkerContextProxy.

These methods should be in WebEmbeddedWorker, because should be called from outside the worker's thread.
They will be implemented in https://codereview.chromium.org/257753002/.

BUG=358657

Review URL: https://codereview.chromium.org/253553002

git-svn-id: svn://svn.chromium.org/blink/trunk@172602 bbb929c8-8fbe-4397-9dbb-9b2b20218538