Worker: Remove ThreadedMessagingProxyBase::WorkerThreadCreated() for cleanup

ThreadedMessagingProxyBase::WorkerThreadCreated() is provided as a virtual
function for DedicatedWorkerMessagingProxy to post queued tasks to the worker
after thread creation. However, DedicatedWorkerMessagingProxy itself initiates
the thread creation in StartWorkerGlobalScope() and can know when it's
available, so such the virtual function is not necessary.

For cleanup, this CL removes WorkerThreadCreated() and inlines posting the
queued tasks in StartWorkerGlobalScope().

Bug: 680046
Change-Id: I5248c78d381e0820461e167249ce89bac93e44a5
Reviewed-on: https://chromium-review.googlesource.com/823052
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523719}
4 files changed