Use Pattern.matchAsPrefix to let String.indexOf/lastIndexOf/startsWith accept Pattern.

sdk/lib/_internal/compiler/implementation/lib/regexp_helper.dart

Index: sdk/lib/_internal/compiler/implementation/lib/regexp_helper.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/regexp_helper.dart b/sdk/lib/_internal/compiler/implementation/lib/regexp_helper.dart
index d2feaa81ee5643a83bdcfab971d401199ca6684d..0e923a3986a17a6771f6be2d6cb1319204be486d 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/regexp_helper.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/regexp_helper.dart
@@ -114,15 +114,15 @@ class JSSyntaxRegExp implements RegExp {
 }
 
 class _MatchImplementation implements Match {
-  final String pattern;
+  final Pattern pattern;
   final String str;
   final int start;
   final int end;
   final List<String> _groups;
 
   const _MatchImplementation(
-      String this.pattern,
-      String this.str,
+      this.pattern,
+      this.str,
       int this.start,
       int this.end,
       List<String> this._groups);
@@ -150,23 +150,46 @@ class _AllMatchesIterable extends IterableBase<Match> {
 }
 
 class _AllMatchesIterator implements Iterator<Match> {
-  final RegExp _re;
-  final String _str;
+  final RegExp _regExp;
+  final RegExp _globalRegExp;
+  String _str;
   Match _current;
 
   _AllMatchesIterator(JSSyntaxRegExp re, String this._str)
-    : _re = new JSSyntaxRegExp._globalVersionOf(re);
+    : _regExp = re,
+      _globalRegExp = new JSSyntaxRegExp._globalVersionOf(re);
 
   Match get current => _current;
 
   bool moveNext() {
+    if (_str == null) return false;
     // firstMatch actually acts as nextMatch because of
     // hidden global flag.
     if (_current != null && _current.start == _current.end) {
       // Advance implicit start-position if last match was empty.
-      JS("void", "#.lastIndex++", regExpGetNative(_re));
+      JS("void", "#.lastIndex++", regExpGetNative(_globalRegExp));
+    }
+    List<String> m =
+        JS('=List|Null', r'#.exec(#)', regExpGetNative(_globalRegExp), _str);
+    if (m == null) {
+      _current = null;
+      _str = null;  // Marks iteration as ended.
+      return false;
     }
-    _current = _re.firstMatch(_str);
-    return _current != null;
+    var matchStart = JS('int', r'#.index', m);
+    var matchEnd = matchStart + m[0].length;
+    _current = new _MatchImplementation(_regExp, _str, matchStart, matchEnd, m);
+    return true;
   }
 }
+
+Match firstMatchAfter(JSSyntaxRegExp re, String str, int start) {
+  JSSyntaxRegExp global = new JSSyntaxRegExp._globalVersionOf(re);
+  JS("void", "#.lastIndex = #", regExpGetNative(global), start);
+  List<String> m =
+      JS('=List|Null', r'#.exec(#)', regExpGetNative(global), checkString(str));
+  if (m == null) return null;
+  var matchStart = JS('int', r'#.index', m);
+  var matchEnd = matchStart + m[0].length;
+  return new _MatchImplementation(re, str, matchStart, matchEnd, m);
+}