src/vs/workbench/api/common/extHostSearch.ts/ExtHostSearch/registerFileSearchProvider
class ExtHostSearch:	registerFileSearchProvider(scheme: string, provider: vscode.FileSearchProvider): IDisposable {
		if (this._fileSearchUsedSchemes.has(scheme)) {
			throw new Error(`a file search provider for the scheme '${scheme}' is already registered`);
		}

		this._fileSearchUsedSchemes.add(scheme);
		const handle = this._handlePool++;
		this._fileSearchProvider.set(handle, provider);
		this._proxy.$registerFileSearchProvider(handle, this._transformScheme(scheme));
		return toDisposable(() => {
			this._fileSearchUsedSchemes.delete(scheme);
			this._fileSearchProvider.delete(handle);
			this._proxy.$unregisterProvider(handle);
		});
	}