Reset user data directory and disk cache directory after downgrade.

chrome/browser/downgrade/user_data_downgrade_browsertest.cc

+// Copyright 2016 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 "chrome/browser/downgrade/user_data_downgrade.h"
+
+#include "base/files/file_util.h"
+#include "base/path_service.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/test/test_reg_util_win.h"
+#include "base/version.h"
+#include "base/win/registry.h"
+#include "chrome/common/chrome_constants.h"
+#include "chrome/common/chrome_paths.h"
+#include "chrome/installer/util/browser_distribution.h"
+#include "chrome/test/base/in_process_browser_test.h"
+#include "content/public/browser/browser_thread.h"
+
+class UserDataDowngradeBrowserTest : public InProcessBrowserTest {
+ protected:
+  void SetUpInProcessBrowserTestFixture() override {
+    SimulateDowngradeForTest(true);
+    HKEY root = HKEY_CURRENT_USER;
+    registry_override_manager_.OverrideRegistry(root);
+    base::win::RegKey key(
+        root, BrowserDistribution::GetDistribution()->GetStateKey().c_str(),
+        KEY_SET_VALUE | KEY_WOW64_32KEY);
+    key.WriteValue(L"DowngradeVersion",
+                   base::ASCIIToUTF16(GetNextChromeVersion()).c_str());
+  }
+
+  // Verify the renamed user data directory has been deleted.
+  void TearDownInProcessBrowserTestFixture() override {
+    const base::FilePath::StringType delete_suffix =
+        FILE_PATH_LITERAL(" (1).CHROME_DELETE");

[sky, 2016/06/03 00:04:24]

Make a constant for this. In fact you should also verify profile is actually
moved to this directory.

[zmin, 2016/06/03 15:46:52]

The moved profile may be deleted very quickly during launch before we are able
to check it.

And it's constant already.

[sky, 2016/06/03 18:18:03]

You need some way to verify all this is working. Add callbacks/observer from the
test if you need to.
By constant I mean the CHROME_DELETE portion. For example, if you change the
name of the mv file this test will continue to succeed no matter what.

+    ASSERT_FALSE(base::DirectoryExists(
+        base::FilePath(user_data_dir_.value() + delete_suffix)));
+    SimulateDowngradeForTest(false);
+  }
+
+  bool SetUpUserDataDirectory() override {
+    const base::FilePath::StringType last_chrome_version_file =
+        FILE_PATH_LITERAL("Last Chrome Version");
+    if (!PathService::Get(chrome::DIR_USER_DATA, &user_data_dir_))
+      return false;
+    if (!CreateTemporaryFileInDir(user_data_dir_, &other_file_))
+      return false;
+    last_chrome_version_path_ = user_data_dir_.Append(last_chrome_version_file);
+    std::string last_chrome_version = GetNextChromeVersion();
+    base::WriteFile(last_chrome_version_path_, last_chrome_version.c_str(),
+                    last_chrome_version.size());
+    return true;
+  }
+
+  std::string GetNextChromeVersion() {
+    return base::Version(std::string(chrome::kChromeVersion) + "1").GetString();
+  }
+
+  base::FilePath last_chrome_version_path_;
+  base::FilePath other_file_;
+  base::FilePath user_data_dir_;
+  registry_util::RegistryOverrideManager registry_override_manager_;
+};
+
+// Verify the user data directory has been renamed and created again after
+// downgrade.
+IN_PROC_BROWSER_TEST_F(UserDataDowngradeBrowserTest, CopyAndClean) {

[sky, 2016/06/03 00:04:24]

Can you also add a test that the directory is not removed if the registry key is
setup?

[zmin, 2016/06/03 15:46:52]

Sure.

+  std::string last_chrome_version_str;
+  base::ReadFileToString(last_chrome_version_path_, &last_chrome_version_str);

[sky, 2016/06/03 00:04:24]

It would be good if user_data_downgrade.h had a specific function for getting
the last version rather than having the test have to read the file.

[zmin, 2016/06/03 15:46:52]

Done.

+  EXPECT_EQ(chrome::kChromeVersion, last_chrome_version_str);
+  ASSERT_FALSE(base::PathExists(other_file_));
+}