This patch fixes a bug in WebIDL code generation that could be triggered
if an input file changed locations but the original file remained on
disk. When computing the set of source .webidl files to perform code
generation on, we failed to prune files that were no longer part of the
active set of input files. References to files in old locations would
get pulled in to the regeneration set, leading to a cryptic KeyError
during code generation.
Previously, the set of WebIDL example interfaces to build was hardcoded
in the mozwebidlcodegen Python package. Unfortunately, the example
interfaces in that set were dependent on test-only bindings files,
resulting in build failures when tests were disabled (because those
test-only bindings were defined in a test directory).
In this patch, we now declare example interfaces in moz.build files
so the set of example interfaces lives next to the set of defined
bindings files. The example interfaces are defined in a test moz.build
file - in the same file declaring the bindings files that contain the
interfaces - so the example interfaces only get picked up if the
corresponding bindings are defined.
We could probably switch WebIDL moz.build variables to use lists with
flags. That would be good followup fodder. For now, let's fix the build.
