[Extensions] Emit metrics for opening a channel for extension messages.

Metrics:
  Extensions.MessagePipeline.OpenChannelStatus{WorkerStatus}{ChannelType}
  Extensions.MessagePipeline.OpenChannelWorkerDispatchStatus{ChannelType}
  Extensions.MessagePipeline.OpenChannelWorkerWakeUpStatus{ChannelType}

This tracks several stages of the initial open channel portion of
sending an extension message.

It tracks each stage of this process as a separate metric. It emits a
relevant value from MessageTracker::OpenChannelMessagePipelineResult
that indicates where the process finishes (or fails).

It also make some minor changes to ServiceWorkerTaskQueue to make it
easier to emit a metric that is worker-based extension specific.

After this change we will be able to determine where in the open channel
process we might be experiencing issues which could contribute to
messages to worker failures.

Low-Coverage-Reason: OTHER message_port.cc DispatchOnConnect non-pure virtual method is empty.
Bug: 371011217
Change-Id: I4ae6628018a4d3d1c2e367244bf787f7db1b326c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5938256
Auto-Submit: Justin Lulejian <jlulejian@chromium.org>
Reviewed-by: Devlin Cronin <rdevlin.cronin@chromium.org>
Commit-Queue: Devlin Cronin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1388520}