src/vs/workbench/api/common/extHostLanguageFeatures.ts/ExtHostLanguageFeatures/registerDeclarationProvider
class ExtHostLanguageFeatures:	registerDeclarationProvider(extension: IExtensionDescription, selector: vscode.DocumentSelector, provider: vscode.DeclarationProvider): vscode.Disposable {
		const handle = this._addNewAdapter(new DeclarationAdapter(this._documents, provider), extension);
		this._proxy.$registerDeclarationSupport(handle, this._transformDocumentSelector(selector));
		return this._createDisposable(handle);
	}