Register thread to WR's profiler and the external profiler.

[JerryShih]

The gecko profiler needs the thread to register itself to gecko profiler before collecting the performance data. In this patch, we have a new "thread listener" interface to do somethings when the thread is created and deleted. Then, we could put the registering function inside the listener interface.

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This change is 

[JerryShih]

The worker_config is only used when we don't have the thread pool. So, move the config into the worker's unwrap_or_else() block.

[JerryShih]

We might have multiple renderer in the same process. Use this renderer_id for identification.

[JerryShih]

Please check:
https://bugzilla.mozilla.org/show_bug.cgi?id=1371838

r? @glennw @kvark

[glennw]

Reviewed 2 of 2 files at r1.
Review status: all files reviewed at latest revision, 3 unresolved discussions.

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webrender/src/renderer.rs, line 1799 at r1 (raw file):

                let worker_config = ThreadPoolConfig::new()
                    .thread_name(|idx|{ format!("WRWorker#{}", idx) })
                    .start_handler(move |idx| {

I think the start and end handlers are only called when the worker thread is created and destroyed. If so, that won't actually be useful for profiling - since we won't know when the thread is doing work or idle?

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webrender/src/renderer.rs, line 1816 at r1 (raw file):

        let blob_image_renderer = options.blob_image_renderer.take();
        let thread_listener_for_render_backend = thread_listener.clone();
        let mut thread_name = String::from("WRRenderBackend");

This could be something like:

let thread_name = format!("WRRenderBackend {}", options.renderer_id.unwrap_or(0));

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Comments from Reviewable

[glennw]

@bors-servo r+

[bors-servo]

📌 Commit e9f943c has been approved by glennw

[glennw]

@bors-servo r+

[bors-servo]

📌 Commit 7c03ad8 has been approved by glennw

[bors-servo]

⌛ Testing commit 7c03ad8 with merge 060a6e6...

[bors-servo]

💔 Test failed - status-travis

[glennw]

@bors-servo retry

[bors-servo]

⌛ Testing commit 7c03ad8 with merge f58ed65...

[bors-servo]

☀️ Test successful - status-appveyor, status-travis
Approved by: glennw
Pushing f58ed65 to master...

[glennw]

Wow, I had not extensively used the Gecko CPU profiler before. It's really excellent - and with this addition we get perfect callstacks for profiling in the WR backend thread. @mrobinson @kvark heads up - next time you need to profile some CPU code in WR, you should try this out! :)

Thanks @JerryShih and others who worked on the patch.