Fix elements transition bug related to array.concat.

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/9358018

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10629 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/builtins.cc

@@ -978,7 +978,7 @@ BUILTIN(ArrayConcat) {
       return CallJsBuiltin(isolate, "ArrayConcat", args);
     }
 
-    if (!JSArray::cast(arg)->HasFastElements()) {
+    if (!JSArray::cast(arg)->HasFastSmiOnlyElements()) {
       elements_kind = FAST_ELEMENTS;
     }
   }

test/mjsunit/regress/regress-smi-only-concat.js

+// Copyright 2012 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Flags: --allow-natives-syntax
+
+// This tests that concatenating a fast smi-only array and a fast object array
+// results in a fast object array.
+
+var fast_array = ['a', 'b'];
+var array = fast_array.concat(fast_array);
+
+assertTrue(%HasFastElements(fast_array));
+assertTrue(%HasFastElements(array));
\ No newline at end of file