Fix FilesystemUtils.SourceDirForPath after r306368

tools/gn/filesystem_utils_unittest.cc

 // Copyright (c) 2013 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/files/file_path.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/filesystem_utils.h"
@@ skipping 398 matching lines @@
             base::FilePath("/source/foo/bar/")).value());
   EXPECT_EQ("//bar/baz/", SourceDirForPath(root,
             base::FilePath("/source/foo/bar/baz/")).value());
 
   // Should be case-sensitive.
   EXPECT_EQ("/SOURCE/foo/bar/", SourceDirForPath(root,
             base::FilePath("/SOURCE/foo/bar/")).value());
 
   // Empty source dir.
   base::FilePath empty;
-  EXPECT_EQ("/source/foo",
+  EXPECT_EQ("/source/foo/",
             SourceDirForPath(empty, base::FilePath("/source/foo")).value());
 #endif
 }
 
 TEST(FilesystemUtils, GetToolchainDirs) {
   BuildSettings build_settings;
   build_settings.SetBuildDir(SourceDir("//out/Debug/"));
 
   // The default toolchain.
   Settings default_settings(&build_settings, "");
@@ skipping 137 matching lines @@
   EXPECT_EQ("gen/", GetToolchainGenDirAsOutputFile(&settings).value());
   EXPECT_EQ("//obj/",
             GetOutputDirForSourceDir(&settings, SourceDir("//")).value());
   EXPECT_EQ("obj/",
             GetOutputDirForSourceDirAsOutputFile(
                 &settings, SourceDir("//")).value());
   EXPECT_EQ("gen/",
             GetGenDirForSourceDirAsOutputFile(
                 &settings, SourceDir("//")).value());
 }