src/vs/platform/contextkey/browser/contextKeyService.ts/ScopedContextKeyService/_updateParentChangeListener
class ScopedContextKeyService:	private _updateParentChangeListener(): void {
		// Forward parent events to this listener. Parent will change.
		this._parentChangeListener.value = this._parent.onDidChangeContext(e => {
			const thisContainer = this._parent.getContextValuesContainer(this._myContextId);
			const thisContextValues = thisContainer.value;

			if (!allEventKeysInContext(e, thisContextValues)) {
				this._onDidChangeContext.fire(e);
			}
		});
	}