Support rollback with installerdata in mini_installer

chrome/installer/util/util_constants.h

 // 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.
 //
 // Defines all install related constants that need to be used by Chrome as
 // well as Chrome Installer.
 
 #ifndef CHROME_INSTALLER_UTIL_UTIL_CONSTANTS_H_
 #define CHROME_INSTALLER_UTIL_UTIL_CONSTANTS_H_
 
@@ skipping 70 matching lines @@
   UNUSED_BINARIES      = 51,  // No multi-install products to update. The
                               // binaries will be uninstalled if they are not
                               // in use.
   UNUSED_BINARIES_UNINSTALLED = 52,  // The binaries were uninstalled.
   UNSUPPORTED_OPTION   = 53,  // An unsupported legacy option was given.
   CPU_NOT_SUPPORTED    = 54,  // Current OS not supported
   REENABLE_UPDATES_SUCCEEDED = 55,  // Autoupdates are now enabled.
   REENABLE_UPDATES_FAILED = 56,  // Autoupdates could not be enabled.
   UNPACKING_FAILED     = 57,  // Unpacking the (possibly patched) uncompressed
                               // archive failed.
+  IN_USE_DOWNGRADE     = 58,  // Successfully downgrade chrome but current

[grt (UTC plus 2), 2016/04/28 16:55:30]

please add these to InstallStatus enum in
tools/metrics/histograms/histograms.xml

[zmin, 2016/04/28 17:51:29]

Done.

+                              // version is still running.
+  OLD_VERSION_DOWNGRADE = 59,  // Successfully downgrade chrome to an older
+                               // version.
 
-  MAX_INSTALL_STATUS = 58,    // Bump this out to make space for new results.
+  MAX_INSTALL_STATUS   = 60,  // Bump this out to make space for new results.
 };
 
 // The type of an update archive.
 enum ArchiveType {
   UNKNOWN_ARCHIVE_TYPE,     // Unknown or uninitialized.
   FULL_ARCHIVE_TYPE,        // Full chrome.7z archive.
   INCREMENTAL_ARCHIVE_TYPE  // Incremental or differential archive.
 };
 
 // Stages of an installation reported through Google Update on failure.
@@ skipping 151 matching lines @@
 extern const char kCourgette[];
 extern const char kBsdiff[];
 
 // Name of the allocator (and associated file) for storing histograms to be
 // reported by Chrome during its next upload.
 extern const char kSetupHistogramAllocatorName[];
 
 }  // namespace installer
 
 #endif  // CHROME_INSTALLER_UTIL_UTIL_CONSTANTS_H_