Add String.replaceFirstMapped.

sdk/lib/_internal/compiler/js_lib/string_helper.dart

Index: sdk/lib/_internal/compiler/js_lib/string_helper.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/string_helper.dart b/sdk/lib/_internal/compiler/js_lib/string_helper.dart
index ff2505729a1b3cce8352be876681941925776479..77b8ab9c34a95b95cb4c4c44604578362ffed8ee 100644
--- a/sdk/lib/_internal/compiler/js_lib/string_helper.dart
+++ b/sdk/lib/_internal/compiler/js_lib/string_helper.dart
@@ -193,21 +193,34 @@ stringReplaceAllStringFuncUnchecked(receiver, pattern, onMatch, onNonMatch) {
 }
 
 
-stringReplaceFirstUnchecked(receiver, from, to, [int startIndex = 0]) {
+stringReplaceFirstUnchecked(receiver, from, to, int startIndex) {
   if (from is String) {
-    var index = receiver.indexOf(from, startIndex);
+    int index = receiver.indexOf(from, startIndex);
     if (index < 0) return receiver;
     return '${receiver.substring(0, index)}$to'
            '${receiver.substring(index + from.length)}';

[sra1, 2015/02/17 17:01:00]

This common pattern (3x) makes me think that we should add

String replaceRange(int start, int end, String replacement)

(It is not quite a natural analog to List.replaceRange since that mutates, but
it is pretty close.)

We should certainly have a local unchecked static function version as the two
substring calls entail a lot of unnecessary validation.

WDYT?

-  } else if (from is JSSyntaxRegExp) {
+  }
+  if (from is JSSyntaxRegExp) {
     return startIndex == 0 ?
         stringReplaceJS(receiver, regExpGetNative(from), to) :
         stringReplaceFirstRE(receiver, from, to, startIndex);
-  } else {
-    checkNull(from);
-    // TODO(floitsch): implement generic String.replace (with patterns).
-    throw "String.replace(Pattern) UNIMPLEMENTED";
   }
+  checkNull(from);
+  Iterator<Match> matches = from.allMatches(receiver, startIndex).iterator;
+  if (!matches.moveNext()) return receiver;
+  Match match = matches.current;
+  return '${receiver.substring(0, match.start)}$to'
+         '${receiver.substring(match.end)}';
+}
+
+stringReplaceFirstMappedUnchecked(receiver, from, replace,
+                                  int startIndex) {
+  Iterator<Match> matches = from.allMatches(receiver, startIndex).iterator;
+  if (!matches.moveNext()) return receiver;
+  Match match = matches.current;
+  String replacement = "${replace(match)}";
+  return '${receiver.substring(0, match.start)}$replacement'
+         '${receiver.substring(match.end)}';
 }
 
 stringJoinUnchecked(array, separator) {