Spelling fixes e to i.

sdk/lib/_internal/js_runtime/lib/js_helper.dart

 // Copyright (c) 2013, 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.
 
 library _js_helper;
 
 import 'dart:_js_embedded_names'
     show
         DEFERRED_LIBRARY_URIS,
         DEFERRED_LIBRARY_HASHES,
@@ skipping 2229 matching lines @@
 /**
  * Called from catch blocks in generated code to extract the Dart
  * exception from the thrown value. The thrown value may have been
  * created by [wrapException] or it may be a 'native' JS exception.
  *
  * Some native exceptions are mapped to new Dart instances, others are
  * returned unmodified.
  */
 unwrapException(ex) {
   /// If error implements Error, save [ex] in [error.$thrownJsError].
-  /// Otherwise, do nothing. Later, the stack trace can then be extraced from
+  /// Otherwise, do nothing. Later, the stack trace can then be extracted from
   /// [ex].
   saveStackTrace(error) {
     if (error is Error) {
       var thrownStackTrace = JS('', r'#.$thrownJsError', error);
       if (thrownStackTrace == null) {
         JS('void', r'#.$thrownJsError = #', error, ex);
       }
     }
     return error;
   }
@@ skipping 1544 matching lines @@
 // unneeded code.
 class _UnreachableError extends AssertionError {
   _UnreachableError();
   String toString() => "Assertion failed: Reached dead code";
 }
 
 @NoInline()
 void assertUnreachable() {
   throw new _UnreachableError();
 }