JS: Format if statements with no else on a single line

lib/runtime/dart/mirrors.js

 dart_library.library('dart/mirrors', null, /* Imports */[
   "dart/_runtime",
   'dart/core'
 ], /* Lazy imports */[
   'dart/_js_mirrors'
 ], function(exports, dart, core, _js_mirrors) {
   'use strict';
   let dartx = dart.dartx;
   class MirrorSystem extends core.Object {
     findLibrary(libraryName) {
       return this.libraries.values[dartx.singleWhere](dart.fn(library => dart.equals(dart.dload(library, 'simpleName'), libraryName), core.bool, [dart.dynamic]));
     }
     static getName(symbol) {
       return _js_mirrors.getName(symbol);
     }
     static getSymbol(name, library) {
-      if (library === void 0)
-        library = null;
+      if (library === void 0) library = null;
       return _js_mirrors.getSymbol(name, library);
     }
   }
   dart.setSignature(MirrorSystem, {
     methods: () => ({findLibrary: [LibraryMirror, [core.Symbol]]}),
     statics: () => ({
       getName: [core.String, [core.Symbol]],
       getSymbol: [core.Symbol, [core.String], [LibraryMirror]]
     }),
     names: ['getName', 'getSymbol']
@@ skipping 102 matching lines @@
   exports.FunctionTypeMirror = FunctionTypeMirror;
   exports.TypeVariableMirror = TypeVariableMirror;
   exports.TypedefMirror = TypedefMirror;
   exports.MethodMirror = MethodMirror;
   exports.VariableMirror = VariableMirror;
   exports.ParameterMirror = ParameterMirror;
   exports.SourceLocation = SourceLocation;
   exports.Comment = Comment;
   exports.MirrorsUsed = MirrorsUsed;
 });