This patch removes support for de-serialization of WebAssembly.Modules. The
preprocessing which was added just for WebAssembly.Modules is not removed since
it can be reused for more efficient de-serialization of big structured clones
which are stored as standalone files. (standalone files can be read and
uncompressed in content process instead of the parent process). So this patch
also adjusts the preprocessing to support that. However the preprocessing is not
fully implemented (we lack support for indexes and cursors) and there's a
theoretical problem with ordering of IDB requests when preprocessing is
involved, so this feature is kept behind a pref for now.

Differential Revision: https://phabricator.services.mozilla.com/D36879

--HG--
rename : dom/indexedDB/test/unit/test_wasm_recompile.js => dom/indexedDB/test/unit/test_wasm_get_values.js
rename : dom/indexedDB/test/unit/wasm_recompile_profile.zip => dom/indexedDB/test/unit/wasm_get_values_profile.zip