src/vs/workbench/api/common/extHostExtensionService.ts/AbstractExtHostExtensionService/getExtensionPathIndex
class AbstractExtHostExtensionService:	public getExtensionPathIndex(): Promise<TernarySearchTree<string, IExtensionDescription>> {
		if (!this._extensionPathIndex) {
			const tree = TernarySearchTree.forPaths<IExtensionDescription>();
			const extensions = this._registry.getAllExtensionDescriptions().map(ext => {
				if (!this._getEntryPoint(ext)) {
					return undefined;
				}
				return this._hostUtils.realpath(ext.extensionLocation.fsPath).then(value => tree.set(URI.file(value).fsPath, ext));
			});
			this._extensionPathIndex = Promise.all(extensions).then(() => tree);
		}
		return this._extensionPathIndex;
	}