foo (1).user.js, not foo.user (1).js.

base/file_path_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/basictypes.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/utf_string_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
@@ skipping 735 matching lines @@
     { FPL("/foo.tar.tar.gz"),        FPL(".tar.gz") },
     { FPL("/foo.tar.gz.gz"),         FPL(".gz.gz") },
     { FPL("."),                      FPL("") },
     { FPL(".."),                     FPL("") },
     { FPL("./foo"),                  FPL("") },
     { FPL("./foo.ext"),              FPL(".ext") },
     { FPL("/foo.ext1/bar.ext2"),     FPL(".ext2") },
     { FPL("/foo.bar////"),           FPL(".bar") },
     { FPL("/foo.bar/.."),            FPL("") },
     { FPL("/foo.bar/..////"),        FPL("") },
+    { FPL("/foo.1234.user.js"),      FPL(".user.js") },
+    { FPL("foo.user.js"),            FPL(".user.js") },
+    { FPL("/foo.1234.luser.js"),     FPL(".js") },
+    { FPL("/user.js"),               FPL(".js") },
   };
   for (unsigned int i = 0; i < arraysize(cases); ++i) {
     FilePath path(cases[i].input);
     FilePath::StringType extension = path.Extension();
     EXPECT_STREQ(cases[i].expected, extension.c_str()) << "i: " << i <<
         ", path: " << path.value();
   }
 }
 
 TEST_F(FilePathTest, InsertBeforeExtension) {
@@ skipping 382 matching lines @@
   };
   for (size_t i = 0; i < arraysize(cases); ++i) {
     FilePath input(cases[i].input);
     FilePath observed = input.NormalizePathSeparators();
     EXPECT_EQ(FilePath::StringType(cases[i].expected), observed.value()) <<
               "i: " << i << ", input: " << input.value();
   }
 }
 
 #endif