Fix EnterpriseDeviceManagementStatus UMA enum, add comments.

components/policy/core/common/policy_loader_win.cc

 // Copyright (c) 2014 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 "components/policy/core/common/policy_loader_win.h"
 
 #include <windows.h>
 #include <lm.h>       // For limits.
 #include <ntdsapi.h>  // For Ds[Un]Bind
 #include <rpc.h>      // For struct GUID
@@ skipping 59 matching lines @@
 const char kExpectedWebStoreUrl[] =
     ";https://clients2.google.com/service/update2/crx";
 // String to be prepended to each blocked entry.
 const char kBlockedExtensionPrefix[] = "[BLOCKED]";
 
 // The GUID of the registry settings group policy extension.
 GUID kRegistrySettingsCSEGUID = REGISTRY_EXTENSION_GUID;
 
 // The list of possible errors that can occur while collecting information about
 // the current enterprise environment.
+// This enum is used to define the buckets for an enumerated UMA histogram.
+// Hence,
+//   (a) existing enumerated constants should never be deleted or reordered, and
+//   (b) new constants should only be appended at the end of the enumeration.
 enum DomainCheckErrors {
   DOMAIN_CHECK_ERROR_GET_JOIN_INFO = 0,
-  DOMAIN_CHECK_ERROR_DS_BIND,
-  DOMAIN_CHECK_ERROR_LAST,
+  DOMAIN_CHECK_ERROR_DS_BIND = 1,
+  DOMAIN_CHECK_ERROR_SIZE,  // Not a DomainCheckError.  Must be last.
 };
 
 // If the LBS extension is found and contains a schema in the registry then this
 // function is used to patch it, and make it compliant. The fix is to
 // add an "items" attribute to lists that don't declare it.
 std::string PatchSchema(const std::string& schema) {
   base::JSONParserOptions options = base::JSON_PARSE_RFC;
   scoped_ptr<base::Value> json(base::JSONReader::Read(schema, options));
   base::DictionaryValue* dict = NULL;
   base::DictionaryValue* properties = NULL;
@@ skipping 203 matching lines @@
   UMA_HISTOGRAM_ENUMERATION("EnterpriseCheck.OSType",
                             base::win::OSInfo::GetInstance()->version_type(),
                             base::win::SUITE_LAST);
 
   // Get the computer's domain status.
   LPWSTR domain;
   NETSETUP_JOIN_STATUS join_status;
   if (NERR_Success != ::NetGetJoinInformation(NULL, &domain, &join_status)) {
     UMA_HISTOGRAM_ENUMERATION("EnterpriseCheck.DomainCheckFailed",
                               DOMAIN_CHECK_ERROR_GET_JOIN_INFO,
-                              DOMAIN_CHECK_ERROR_LAST);
+                              DOMAIN_CHECK_ERROR_SIZE);
     return;
   }
   ::NetApiBufferFree(domain);
 
   bool in_domain = join_status == NetSetupDomainName;
   UMA_HISTOGRAM_BOOLEAN("EnterpriseCheck.InDomain", in_domain);
   if (in_domain) {
     // This check will tell us how often are domain computers actually
     // connected to the enterprise network while Chrome is running.
     HANDLE server_bind;
     if (ERROR_SUCCESS == ::DsBind(NULL, NULL, &server_bind)) {
       UMA_HISTOGRAM_COUNTS("EnterpriseCheck.DomainBindSucceeded", 1);
       ::DsUnBind(&server_bind);
     } else {
       UMA_HISTOGRAM_ENUMERATION("EnterpriseCheck.DomainCheckFailed",
                                 DOMAIN_CHECK_ERROR_DS_BIND,
-                                DOMAIN_CHECK_ERROR_LAST);
+                                DOMAIN_CHECK_ERROR_SIZE);
     }
   }
 }
 
 }  // namespace
 
 const base::FilePath::CharType PolicyLoaderWin::kPRegFileName[] =
     FILE_PATH_LITERAL("Registry.pol");
 
 PolicyLoaderWin::PolicyLoaderWin(
@@ skipping 311 matching lines @@
 
 void PolicyLoaderWin::OnObjectSignaled(HANDLE object) {
   DCHECK(object == user_policy_changed_event_.handle() ||
          object == machine_policy_changed_event_.handle())
       << "unexpected object signaled policy reload, obj = "
       << std::showbase << std::hex << object;
   Reload(false);
 }
 
 }  // namespace policy