ObjectActor.prototype.grip is currently failing because Cu is not available in the worker context.

Notes from slack

there's this kind of weird logic when we look at typed arrays to get the length while skipping over any overridden own 'length' property on the typed array

there are a couple problems here imo
1) the tab shouldn't crash! the wrapping code should throw instead of taking down the process
2) this logic seems unnecessary. if someone wants to override 'length' to do something weird, it seems like the debugger should respect that when displaying the typed array's contents
the offending logic is in getArrayLength in devtools/server/actors/object/utils.js

This patch fixes previewing in workers for Array, TypedArray, Set, and Map. WeakSet and WeakMap are still broken --- they rely on some ChromeUtils interfaces which ought to be available in workers, but I haven't figured out how to actually access them here. Other previewers should work as expected. I'll try to write a test for these changes before landing.

Backed out for failing xpcshell at test_framebindings-02.js

Push with failures: https://treeherder.mozilla.org/#/jobs?repo=mozilla-inbound&resultStatus=testfailed%2Cbusted%2Cexception&classifiedState=unclassified&selectedJob=230908989&revision=67bef7d63d865cd66c8f7c836ed8a0b90da8215e

Failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=230908989&repo=mozilla-inbound&lineNumber=2010

Backout: https://hg.mozilla.org/integration/mozilla-inbound/rev/d11fd5d6bda6aca0e7e5786a45471726dfdddb9a

https://hg.mozilla.org/mozilla-central/rev/4047bcadec73

Backed out changeset 4047bcadec73 (Bug 1522244) for mochitest failure at devtools/client/debugger/new/test/mochitest/browser_dbg-worker-scopes.js a=backout

Push with failures: https://hg.mozilla.org/integration/mozilla-inbound/rev/4047bcadec73

Failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=231330045&repo=mozilla-inbound&lineNumber=24220
and https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=231329937&repo=mozilla-inbound&lineNumber=24442

21:15:55 INFO - TEST-PASS | devtools/client/debugger/new/test/mochitest/browser_dbg-worker-scopes.js | "two" -
21:15:55 INFO - Leaving test bound
21:15:55 INFO - Buffered messages logged at 13:15:55
21:15:55 INFO - Removing tab.
21:15:55 INFO - Waiting for event: 'TabClose' on [object XULElement].
21:15:55 INFO - Got event: 'TabClose' on [object XULElement].
21:15:55 INFO - Tab removed and finished closing
21:15:55 INFO - Buffered messages finished
21:15:55 INFO - TEST-UNEXPECTED-FAIL | devtools/client/debugger/new/test/mochitest/browser_dbg-worker-scopes.js | A promise chain failed to handle a rejection: Current state is running - stack: updateWorkers/<@resource://devtools/client/debugger/new/src/actions/debuggee.js:11:5
21:15:55 INFO - asyncthunk/</</<@resource://devtools/client/debugger/new/src/actions/utils/middleware/thunk.js:21:45
21:15:55 INFO - bindActionCreator/<@resource://devtools/client/shared/vendor/redux.js:644:12
21:15:55 INFO - workerListChanged@resource://devtools/client/debugger/new/src/client/firefox/events.js:89:11
21:15:55 INFO - emit@resource://devtools/shared/event-emitter.js:186:24
21:15:55 INFO - emit@resource://devtools/shared/event-emitter.js:267:18
21:15:55 INFO - onPacket@resource://devtools/shared/protocol.js:1424:13
21:15:55 INFO - onPacket@resource://devtools/shared/client/debugger-client.js:601:13
21:15:55 INFO - send/<@resource://devtools/shared/transport/local-transport.js:64:23
21:15:55 INFO - exports.makeInfallible/<@resource://devtools/shared/ThreadSafeDevToolsUtils.js:109:22
21:15:55 INFO - DevToolsUtils.executeSoonexports.executeSoon@resource://devtools/shared/DevToolsUtils.js:55:21
21:15:55 INFO - send@resource://devtools/shared/transport/local-transport.js:58:21
21:15:55 INFO - send@resource://devtools/server/main.js:1023:20
21:15:55 INFO - receiveMessage@resource://devtools/shared/transport/child-transport.js:66:16
21:15:55 INFO - MessageListener.receiveMessage*_addListener@resource://devtools/shared/transport/child-transport.js:40:14
21:15:55 INFO - ready@resource://devtools/shared/transport/child-transport.js:57:10
21:15:55 INFO - connectToFrame/</onActorCreated<@resource://devtools/server/main.js:730:24
21:15:55 INFO - exports.makeInfallible/<@resource://devtools/shared/ThreadSafeDevToolsUtils.js:109:22
21:15:55 INFO - MessageListener.receiveMessagetrackMessageManager@resource://devtools/server/main.js:612:14
21:15:55 INFO - connectToFrame/<@resource://devtools/server/main.js:825:7
21:15:55 INFO - connectToFrame@resource://devtools/server/main.js:601:12
21:15:55 INFO - connect@resource://devtools/server/actors/targets/frame-proxy.js:57:36
21:15:55 INFO - asyncBrowserTabList.prototype._getActorForBrowser@resource://devtools/server/actors/webbrowser.js:313:16

https://hg.mozilla.org/mozilla-central/rev/faddaf06f46c

I see WeakMap/WeakSet were mentioned here but I don't see it tracked so I filed https://bugzilla.mozilla.org/show_bug.cgi?id=1533202, feel free to dup if it already exists though.

I don't think

object.proto.proto.getOwnPropertyDescriptor("length").get

is reliable. The [[Prototype]] of the typed array could have been altered.
Same for callPropertyOnObject.