Replaces the (temporary) compile-time option to pass engine switches
with the ability to pass them temporarily at runtime via environment
variables. This moves the recently-added code for doing this on Windows
to a shared location for use by all desktop embeddings.
This is enabled only for debug/profile to avoid potential issues with
tampering with released applications, but if there is a need for that in
the future it could be added (potentially with a whitelist, as is
currently used for Dart VM flags).
Temporarily adds a way to enable mirrors as a compile time option,
as is already provided in the Linux embedding, to provide a migration
path for the one remaining known need for compile-time options
that has been raised in flutter/flutter#38569.
Replaces the (temporary) compile-time option to pass engine switches
with the ability to pass them temporarily at runtime via environment
variables.
This is enabled only for debug/profile to avoid potential issues with
tampering with released applicaitons, but if there is a need for that in
the future it could be added (potentially with a whitelist, as is
currently used for Dart VM flags).
Windows portion of:
https://github.com/flutter/flutter/issues/38569https://github.com/flutter/flutter/issues/60393
Refactors the Windows embedding internals to make an engine object that
owns things associated with the engine rather than the view, and updates
the API surface to allow using the engine directly.
This is an incremental step toward both a cleaner, non-struct-based
internal structure and a finalized API surface.
