Test checking for DEBUGGER_READY and DEVTOOLS_LOAD events failing

[elliette]

In #2388 we switched to connecting to DDS instead of directly to the VMService so that DDS can handle the service extensions.

However, the test checking that the DEBUGGER_READY and DEVTOOLS_LOAD events are sent when DevTools is opened has begun failing. When I launch DevTools to do manually testing, I do see the service extension ext.dwds.sendEvent is correctly being called, and these events are being emitted, so I don't think this is a regression with the feature.

Need to follow-up to figure out what changes are required to get the test to pass again.

[bkonyi]

Marking as P3 since there's no obvious issues in production, only this test failure.