GitLab

JS can be suspended when the renderer receives the IPC to dispatch an
event. In this case, the JS shouldn't immediately run, but rather
respect the JS state. Currently, the EventEmitter does this by using
JSRunner::RunJSFunction() (which does respect JS suspension) with each
of the listeners for the event.

This mostly works, but has a couple of problems. For one, it makes it
difficult to catch exceptions thrown from a JS listener (since the
listener isn't notified when we queue it up through the JSRunner). It
also doesn't account for the possibility of listeners being removed
between a event comes in, and when it is actually disptached. Finally,
it makes creating a single result for the dispatch difficult, which is
problematic for messaging bindings.

Rework the way event dispatching works to instead use a v8::Function
wrapper around the EventEmitter to trigger the event being dispatched
to listeners. Once that function is triggered, it's safe to use
synchronous JS execution, since JS is already running at that point.
This addresses the concerns with the current approach.

Also add a Suspension utility to the TestJSRunner to simulate JS being
suspended in testing, and add unit tests for dispatching events while
JS is suspended.

Bug: 653596

Change-Id: I7899e1946e8fe750fa2a1f53d62a04e5bd075664
Reviewed-on: https://chromium-review.googlesource.com/792033
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521592}