Remove support for String operator + from dart2js.

dart/lib/compiler/implementation/lib/mockimpl.dart

Index: dart/lib/compiler/implementation/lib/mockimpl.dart
diff --git a/dart/lib/compiler/implementation/lib/mockimpl.dart b/dart/lib/compiler/implementation/lib/mockimpl.dart
index b6f18055e7e65737ee6033ffd3f0a97f538179ab..fd6d6e1c978213ff68b52e2e82d22f112418dcf2 100644
--- a/dart/lib/compiler/implementation/lib/mockimpl.dart
+++ b/dart/lib/compiler/implementation/lib/mockimpl.dart
@@ -142,27 +142,35 @@ class StringBase {
   static String join(List<String> strings, String separator) {
     checkNull(strings);
     checkNull(separator);
-    var result = "";
-    var first = true;
-    for (var string in strings) {
-      checkNull(string);
-      if (string is !String) throw new IllegalArgumentException(string);
-      if (!first) result += separator; // TODO(ahe): Use string buffer.
-      result += string; // TODO(ahe): Use string buffer.
-      first = false;
-    }
-    return result;
+    if (separator is !String) throw new IllegalArgumentException(separator);
+    return stringJoinUnchecked(_toJsStringArray(strings), separator);
   }
 
   static String concatAll(List<String> strings) {
+    return stringJoinUnchecked(_toJsStringArray(strings), "");
+  }
+
+  static List _toJsStringArray(List<String> strings) {
     checkNull(strings);
-    var result = "";
-    for (var string in strings) {
-      checkNull(string);
-      if (string is !String) throw new IllegalArgumentException(string);
-      result = '$result$string'; // TODO(ahe): Use string buffer.
+    var array;
+    final length = strings.length;
+    if (isJsArray(strings)) {
+      array = strings;
+      for (int i = 0; i < length; i++) {
+        final string = strings[i];
+        checkNull(string);

[Lasse Reichstein Nielsen, 2012/06/18 09:25:32]

Do we really want to throw a NPE instead of an IAE in this case? Null us just an
invalid argument too.

[ahe, 2012/06/18 10:39:16]

This is what the other implementation does. I cannot pass co19 tests unless I
check this.

If you think this is problematic, document the API. As long as the API is
virtually unspecified, the co19 test writers had to guess the specification
based on early implementations.

+        if (string is !String) throw new IllegalArgumentException(string);
+      }
+    } else {
+      array = new List(length);
+      for (int i = 0; i < length; i++) {
+        final string = strings[i];
+        checkNull(string);
+        if (string is !String) throw new IllegalArgumentException(string);
+        array[i] = string;
+      }
     }
-    return result;
+    return array;
   }
 }