Small cleanups in RegExp to avoid generating lots of code just because there is a try/catch in our …

sdk/lib/core/regexp.dart

Index: sdk/lib/core/regexp.dart
===================================================================
--- sdk/lib/core/regexp.dart	(revision 19035)
+++ sdk/lib/core/regexp.dart	(working copy)
@@ -94,6 +94,8 @@
   /**
    * Constructs a regular expression. The default implementation of a
    * [RegExp] sets [multiLine] to false and [caseSensitive] to true.
+   * Throws a [FormatException] if [pattern] is not a valid regular
+   * exression pattern.
    */
   external factory RegExp(String pattern, {bool multiLine: false,
                                            bool caseSensitive: true});