- GET_NATIVE_ARGUMENT uses the isolate which is passed in to allocate the handle.

runtime/lib/string.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * [StringBase] contains common methods used by concrete String implementations,
  * e.g., OneByteString.
  */
 class StringBase {
 
@@ skipping 214 matching lines @@
     }
     return buffer.add(this.substring(startIndex)).toString();
   }
 
   /**
    * Convert all objects in [values] to strings and concat them
    * into a result string.
    */
   static String _interpolate(List values) {
     int numValues = values.length;
-    List<String> stringList = new List<String>(numValues);
-    int resultLength = 0;
+    var stringList = new ObjectArray(numValues);
     for (int i = 0; i < numValues; i++) {
-      String str = values[i].toString();
-      resultLength += str.length;
-      stringList[i] = str;
+      stringList[i] = values[i].toString();
     }
-    List<int> codepoints = new List<int>(resultLength);
-    int intArrayIx = 0;
-    for (int i = 0; i < numValues; i++) {
-      String str = stringList[i];
-      int strLength = str.length;
-      for (int k = 0; k < strLength; k++) {
-        codepoints[intArrayIx++] = str.charCodeAt(k);
-      }
-    }
-    return StringBase.createFromCharCodes(codepoints);
+    return _concatAll(stringList);
   }
 
   Iterable<Match> allMatches(String str) {
     List<Match> result = new List<Match>();
     int length = str.length;
     int patternLength = this.length;
     int startIndex = 0;
     while (true) {
       int position = str.indexOf(this, startIndex);
       if (position == -1) {
@@ skipping 229 matching lines @@
     for (int g in groups) {
       result.add(group(g));
     }
     return result;
   }
 
   final int _start;
   final String str;
   final String pattern;
 }