Fix last-minute-typo.

runtime/lib/string_patch.dart

Index: runtime/lib/string_patch.dart
diff --git a/runtime/lib/string_patch.dart b/runtime/lib/string_patch.dart
index 12d788deb0f98278d5081ba528379edee31e3e72..f584410861cc4f8838a07be46a853edcf68e5801 100644
--- a/runtime/lib/string_patch.dart
+++ b/runtime/lib/string_patch.dart
@@ -729,11 +729,11 @@ class _StringBase {
     if (match.end < this.length) {
       length += _addReplaceSlice(slices, match.end, this.length);
     }
-    bool replacementIsOneByte = _replacement._isOneByte;
+    bool replacementIsOneByte = replacement._isOneByte;
     if (replacementIsOneByte &&
         length < _maxJoinReplaceOneByteStringLength &&
         this._isOneByte) {
-      return _joinReplaceAllOneByteResult(this, matches, length);
+      return _joinReplaceAllOneByteResult(this, slices, length);
     }
     return _joinReplaceAllResult(this, slices, length, replacementIsOneByte);
   }