Make embedding + V8 inspector work again

[bnoordhuis]

See #16981 (comment).

Commit 9e08695 removed all v8::platform::PumpMessageLoop() calls from the code base.

It's problematic for embedders like electron that plug in their own v8::Platform because they now no longer get notifications from the V8 inspector.

We should probably restore the PumpMessageLoop() calls, even if they're no-ops in normal node builds.

[jasnell]

sgtm

[refack]

+1
We could coordinate with @zcbenz and rollback 2728112 congruent with this fix.

[addaleax]

I wouldn’t personally agree with rolling back 2728112. If we want ourselves or embedders to be able to run multiple isolates in a single process in some way, now or at some point in the future, then the default platform is not going to work for that because it doesn’t allow de-registering Isolates.

[zcbenz]

I would be happy to try whether your fix would work in Electron.

[bnoordhuis]

@zcbenz Can you describe in a few words what the ideal electron + node integration would look like? I remember you used to have trouble integrating with the libuv event loop. Perhaps we can work out something better now.

If you want something a little less open-ended: who should sit at the bottom of the call stack, node or electron? Who should call uv_run()?

[levimm]

@bnoordhuis I'll try to rephrase my issue.
I'm using v8::platform::CreateDefaultPlatform in embedding and it requires link to v8_libplatform.lib. I get this v8_libplatform.lib by building nodejs v9.0.0. If I upgrade node to 9.1.0, the addon will fail to work since I need to build a new v8_libplatform again.
I'm not sure if this is the right way of doing this.

[MylesBorins]

/cc @nodejs/v8

[zcbenz]

@zcbenz Can you describe in a few words what the ideal electron + node integration would look like? I remember you used to have trouble integrating with the libuv event loop. Perhaps we can work out something better now.

Basically we create a new thread to watch events of the backend fd of the uv loop, when there is a new event, we would notify the main thread and call uv_run_once in the main thread.

A simplified version of node integration can be found at https://github.com/yue/yode/blob/master/src/node_integration.cc.

[levimm]

@bnoordhuis Hi, any news on this topic (bring PumpMessageLoop back)?

[bnoordhuis]

@levimm Not at the moment. I don't have time to work on it myself but I can mentor and review pull requests, if you like.