Reset user data directory and disk cache directory after downgrade.

chrome/installer/util/install_util.h

Index: chrome/installer/util/install_util.h
diff --git a/chrome/installer/util/install_util.h b/chrome/installer/util/install_util.h
index 79b8e2a2304f8755ce5a038b18da275ec1ddd017..8a15a013a50663afb18591dcbcf9403f227a84ce 100644
--- a/chrome/installer/util/install_util.h
+++ b/chrome/installer/util/install_util.h
@@ -183,6 +183,21 @@ class InstallUtil {
   // Returns a string in the form YYYYMMDD of the current date.
   static base::string16 GetCurrentDate();
 
+  // Return downgrade version if the value exists or empty version.
+  static base::Version GetDowngradeVersion(HKEY root);
+
+  // Add downgrade version into registry if the value does not exist. This
+  // function should only be called for Chrome install.
+  static void AddSetDowngradeVersionItem(HKEY root,
+                                         const base::Version& existing_version,
+                                         WorkItemList* list);
+
+  // Remove downgrade version from registry if the value exists. The function
+  // should only be called for Chrome install.
+  static void AddRemoveDowngradeVersionItem(HKEY root,
+                                            const base::Version& new_version,
+                                            WorkItemList* list);
+
   // A predicate that compares the program portion of a command line with a
   // given file path.  First, the file paths are compared directly.  If they do
   // not match, the filesystem is consulted to determine if the paths reference