[37588] added methods to backup the plugin globals, for ensuring that advanced cache drop-ins don't overwrite hooks that've been added earlier in the load process.
The method for restoring the plugin globals wasn't compatible with the implementation of `WP_Hook` in #17817. `WP_Hook` implements `ArrayAccess`, so `_restore_plugin_globals()` was treating it as an array, and inadvertantly overwriting the `WP_Hook` object with a plain array.
To avoid having to re-write this code as part of #17817, we now use `add_filter()` to restore any hooks that were added by cache drop-ins, which `WP_Hook` correctly supports.
Props pento, jorbin.
See #36819.
git-svn-id: https://develop.svn.wordpress.org/trunk@38223 602fd350-edb4-49c9-b593-d223f7449a82
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