Add optional start index to Pattern.allMatches.

sdk/lib/_internal/lib/string_helper.dart

Index: sdk/lib/_internal/lib/string_helper.dart
diff --git a/sdk/lib/_internal/lib/string_helper.dart b/sdk/lib/_internal/lib/string_helper.dart
index e3fb93b40470279eb685584a98d8114f5d36849b..c134844a30c98dff720ac7b0f4920fde9688a661 100644
--- a/sdk/lib/_internal/lib/string_helper.dart
+++ b/sdk/lib/_internal/lib/string_helper.dart
@@ -33,13 +33,13 @@ class StringMatch implements Match {
   final String pattern;
 }
 
-List<Match> allMatchesInStringUnchecked(String needle, String haystack) {
+List<Match> allMatchesInStringUnchecked(String needle, String haystack,
+                                        int startIndex) {
   // Copied from StringBase.allMatches in
   // /runtime/lib/string_base.dart
   List<Match> result = new List<Match>();
   int length = haystack.length;
   int patternLength = needle.length;
-  int startIndex = 0;
   while (true) {
     int position = haystack.indexOf(needle, startIndex);
     if (position == -1) {