password_manager bad_message.h: Use a sparse histogram.

components/password_manager/content/browser/bad_message.h

 // Copyright 2015 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.
 
 #ifndef COMPONENTS_PASSWORD_MANAGER_CONTENT_BROWSER_BAD_MESSAGE_H_
 #define COMPONENTS_PASSWORD_MANAGER_CONTENT_BROWSER_BAD_MESSAGE_H_
 
 namespace content {
 class RenderProcessHost;
 }
 
 namespace password_manager {
 // The browser process often chooses to terminate a renderer if it receives
 // a bad IPC message. The reasons are tracked for metrics.
 //
 // See also content/browser/bad_message.h.
 //
 // NOTE: Do not remove or reorder elements in this list. Add new entries at the
 // end. Items may be renamed but do not change the values. We rely on the enum
-// values in histograms. Also update histograms.xml with any new values by
-// running:
-//    python tools/metrics/histograms/update_bad_message_reasons.py
+// values in histograms.
 enum class BadMessageReason {
   CPMD_BAD_ORIGIN_FORMS_PARSED = 1,
   CPMD_BAD_ORIGIN_FORMS_RENDERED = 2,
   CPMD_BAD_ORIGIN_FORM_SUBMITTED = 3,
   CPMD_BAD_ORIGIN_FOCUSED_PASSWORD_FORM_FOUND = 4,
   CPMD_BAD_ORIGIN_IN_PAGE_NAVIGATION = 5,
   CPMD_BAD_ORIGIN_PASSWORD_NO_LONGER_GENERATED = 6,
 
   // Please add new elements here. The naming convention is abbreviated class
   // name (e.g. ContentPasswordManagerDriver becomes CPMD) plus a unique
-  // description of the reason.
+  // description of the reason. After making changes, you MUST update
+  // histograms.xml by running:
+  // "python tools/metrics/histograms/update_bad_message_reasons.py"
   BAD_MESSAGE_MAX
 };
 
 namespace bad_message {
 // Called when the browser receives a bad IPC message from a renderer process on
 // the UI thread. Logs the event, records a histogram metric for the |reason|,
 // and terminates the process for |host|.
 void ReceivedBadMessage(content::RenderProcessHost* host,
                         BadMessageReason reason);
 
 }  // namespace bad_message
 }  // namespace password_manager
 
 #endif  // COMPONENTS_PASSWORD_MANAGER_CONTENT_BROWSER_BAD_MESSAGE_H_