src/vs/workbench/services/extensions/common/extensionDescriptionRegistry.ts/ExtensionDescriptionRegistry/keepOnly
class ExtensionDescriptionRegistry:	public keepOnly(extensionIds: ExtensionIdentifier[]): void {
		const toKeep = new Set<string>();
		extensionIds.forEach(extensionId => toKeep.add(ExtensionIdentifier.toKey(extensionId)));
		this._extensionDescriptions = this._extensionDescriptions.filter(extension => toKeep.has(ExtensionIdentifier.toKey(extension.identifier)));
		this._initialize();
		this._onDidChange.fire(undefined);
	}