As part of reusing the block utility object, asynchronous say block
functions cannot use the utility in a promise or timeout asynchronous
handle. Store the needed target reference so utility is not needed
later.
blockUtility as an object literal inside execute creates 11 objects,
one for the object, and 10 for the function closures. As a separate
object and allocated once, setting its sequencer and thread members,
block functions can share the same util object. Extract blockUtility to
cut down on allocations.
`handleReport` inside `src/engine/execute.js`'s `execute` method needs
to allocate a closure to be able to refer to the higher scoped
variables. `execute` is called frequently that this has a noticable
impact on memory allocation and later collection. Extract handleReport
and add arguments to prevent the allocation.
- Accumulate extension info while deserializing JSON
- Install extensions (if any) before installing target(s)
- Merged 'install' steps of the "add sprite" and "load project" paths
Since we will only have builtin extensions for a while, the
more-complicated, watchdog-based extension duplication prevention has
been replaced with one that treats the extension URL as equivalent to
the extension ID. This is true only for built-in extensions, so once we
start supporting third-party extensions we will likely need to bring
back the watchdog (commit e4381b4693) and
the more-complex duplication prevention (commit
670e51d335).
The code here should be treated as a last resort: ideally the GUI should
check if a particular extension is loaded (maybe by calling the
Extension Manager's new `isExtensionLoaded` method) and avoid calling
`loadExtensionURL` if it is.
If an extension attempts to register with the same ID as another
extension which has already registered, the new registration is refused.
If the extension is in a worker and no other extension is successfully
registered by that worker, the watchdog system will terminate the
"empty" worker.
If an extension worker does not complete initialization in a reasonable
amount of time (currently 15 seconds) then the worker will be
terminated. A complete initialization includes registering an extension.
