Previously we were inconsistent by generating code for enum definitions
but not generating code for dictionaries. With future changes to the
IDL generator to expose helpers to convert to and from IDL values
this produced circular depdendencies. To solve this problem, also
generate the dictionary definitions in bindings headers.
This is largely editorial. One behaviour change is that events are now
sent from a global task on the DOMManipulation task source.
Somewhat awkwardly, the spec refers to `this` before the Worker exists.
As it's for getting the relevant global object / settings object, I've
had to work around that.
Corresponds to:
917c2f6a73
Shared workers are essentially just workers that may be accessed from
scripts within the same origin. There are plenty of FIXMEs here (mostly
building on existing worker FIXMEs that are already in place), but this
lets us run the shared worker variants of WPT tests.
