When trying to print the scope information for the class fields
initializer function, the debugger asks the parser to parse the class
literal as a function literal (to get the scope info) ... which
doesn't quite work.

Instead of adding support for parsing the class literal, we just short
cicruit this parsing step by just returning an empty context.

This works fine because initializer function doesn't have any
variables in it's local scope.

The one caveat is that the objects in the scope above this function
(like the global) are now missing. This trade off is possibly fine
for now, as adding parsing support for class literal to only produce
would be a lot of code for not enough use.

As a follow up to this change, the devtools UI needs to be updated to
handle this empty context cleanly. Currently, it doesn't show the
`this` object if no context exists even if the `this` object is
correctly passed to the UI from the backend.

Bug: v8:5367, v8:8122
Cq-Include-Trybots: luci.chromium.try:linux_chromium_headless_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I52965f26241bbf6abdc988783aa0fc44bb36901f
Reviewed-on: https://chromium-review.googlesource.com/c/1274268
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56611}