Support a subset of String.format in java2dart.

editor/util/plugins/com.google.dart.java2dart/resources/java_core.dart

Index: editor/util/plugins/com.google.dart.java2dart/resources/java_core.dart
diff --git a/editor/util/plugins/com.google.dart.java2dart/resources/java_core.dart b/editor/util/plugins/com.google.dart.java2dart/resources/java_core.dart
index 0c40a7e867d9c80e0a0325b580ca5fff8e470570..063c7d59ce7d3b6097c90dce01cdee14305f1f7f 100644
--- a/editor/util/plugins/com.google.dart.java2dart/resources/java_core.dart
+++ b/editor/util/plugins/com.google.dart.java2dart/resources/java_core.dart
@@ -130,7 +130,18 @@ class CharBuffer extends CharSequence {
 
 class JavaString {
   static String format(String fmt, List args) {
-    return fmt;
+    var index = 0;
+    return fmt.replaceAllMapped(new RegExp(r'%(.)'), (match) {
+      switch (match.group(1)) {
+        case '%': return '%';
+        case 's':
+          if (index >= args.length) {
+            throw new MissingFormatArgumentException(match.group(0));
+          }
+          return args[index++].toString();
+        default: return match.group(1);
+      }
+    });
   }
 }
 
@@ -263,6 +274,14 @@ class IOException implements Exception {
   String toString() => "IOException";
 }
 
+class MissingFormatArgumentException implements Exception {
+  final String s;
+
+  String toString() => "MissingFormatArgumentException: $s";
+
+  MissingFormatArgumentException(this.s);
+}
+
 class ListWrapper<E> extends ListBase<E> implements List<E> {
   List<E> elements = new List<E>();