Reset user data directory and disk cache directory after downgrade.

chrome/browser/policy/policy_path_parser.h

Index: chrome/browser/policy/policy_path_parser.h
diff --git a/chrome/browser/policy/policy_path_parser.h b/chrome/browser/policy/policy_path_parser.h
index 7f4bab1235c8e7870d0dc6c9be11f34dabc61587..270f23aabc2f4585e6e1bee174cdeb4a6729a7e2 100644
--- a/chrome/browser/policy/policy_path_parser.h
+++ b/chrome/browser/policy/policy_path_parser.h
@@ -64,6 +64,15 @@ base::FilePath::StringType ExpandPathVariables(
 // account.
 void CheckUserDataDirPolicy(base::FilePath* user_data_dir);
 
+#if defined(OS_WIN)

[grt (UTC plus 2), 2016/05/19 23:39:27]

although it's only used on Win, it's cleaner to declare/define it on all
platforms

[zmin, 2016/05/20 00:52:25]

Done. But I'll leave Linux/Mac version as unimplemented because no one will use
this function on those platform.

[grt (UTC plus 2), 2016/05/20 15:25:04]

Acknowledged.

+// A helper function used to read the DiskCacheDir path policy without relying
+// on any policy infrastructure. This is required because this policy may be
+// needed much earlier before the PrefService is initialized on Windows.
+// The function will fill |disk_cache_dir| if the policy "DiskCacheDir" is set
+// and leave it intact if the policy is missing.
+void CheckDiskCacheDirPolicy(base::FilePath* disk_cache_dir);
+#endif
+
 }  // namespace path_parser
 
 }  // namespace policy