Translate: Fix broken UMA entries

chrome/browser/translate/translate_browser_metrics.h

 // Copyright 2013 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 CHROME_BROWSER_TRANSLATE_TRANSLATE_BROWSER_METRICS_H_
 #define CHROME_BROWSER_TRANSLATE_TRANSLATE_BROWSER_METRICS_H_
 
 #include <string>
 
 namespace TranslateBrowserMetrics {
 
 // An indexing type to query each UMA entry name via GetMetricsName() function.
 // Note: |kMetricsEntries| should be updated when a new entry is added here.
 enum MetricsNameIndex {
   UMA_INITIATION_STATUS,
   UMA_LANGUAGE_DETECTION_ERROR,
   UMA_LOCALES_ON_DISABLED_BY_PREFS,
   UMA_UNDISPLAYABLE_LANGUAGE,
   UMA_UNSUPPORTED_LANGUAGE_AT_INITIATION,
   UMA_MAX,
 };
 
 // When Chrome Translate is ready to translate a page, one of following reason
 // decide the next browser action.
+// Note: Don't insert any item. It will change reporting UMA value, and break
+// the UMA dashboard page. Insteads, append it at the end of enum as suggested
+// below.

[Ilya Sherman, 2013/11/05 00:04:59]

It looks like this change will break the histogram; or else that previously
uploaded data to this histogram was incorrect.  Either way, your histogram will
now have mixed data, which is a pain to work with.  I'd strongly encourage you
rename the live histogram, and mark the old name as <obsolete> in
histograms.xml.

[Takashi Toyoshima, 2013/11/05 00:18:27]

Actually, it was already broken, and this change is going to revert the broken
order. Then,even so do you think that renaming is better?

Also I have one question. If I make a change against XML, does it affects to UMA
dashboard immediately? Does it affects to all dashboard results including old
one which were aggregated before the XML change?

[Ilya Sherman, 2013/11/05 00:20:58]

If it was already broken, then you already have polluted data that has been
uploaded to the server and that is reflected on the dashboard.  There will
always be clients stuck on the versions that had the broken logic, so the data
will be polluted forever from now on.  Hence, I do recommend renaming the
histogram and obsoleting the current name.
Yes, changes to the XML are picked up more or less immediately, and affect all
data, past, present, and future.

 enum InitiationStatusType {
   INITIATION_STATUS_DISABLED_BY_PREFS,
   INITIATION_STATUS_DISABLED_BY_SWITCH,
   INITIATION_STATUS_DISABLED_BY_CONFIG,
   INITIATION_STATUS_LANGUAGE_IS_NOT_SUPPORTED,
-  INITIATION_STATUS_MIME_TYPE_IS_NOT_SUPPORTED,
   INITIATION_STATUS_URL_IS_NOT_SUPPORTED,
   INITIATION_STATUS_SIMILAR_LANGUAGES,
   INITIATION_STATUS_ACCEPT_LANGUAGES,
-
   INITIATION_STATUS_AUTO_BY_CONFIG,
   INITIATION_STATUS_AUTO_BY_LINK,
   INITIATION_STATUS_SHOW_INFOBAR,
-
+  INITIATION_STATUS_MIME_TYPE_IS_NOT_SUPPORTED,
+  // Insert new item here.

[Ilya Sherman, 2013/11/05 00:04:59]

nit: "new item" -> "new items"

[Takashi Toyoshima, 2013/11/05 01:31:04]

Done.

   INITIATION_STATUS_MAX,
 };
 
 // Called when Chrome Translate is initiated to report a reason of the next
 // browser action.
 void ReportInitiationStatus(InitiationStatusType type);
 
 // Called when Chrome opens the URL so that the user sends an error feedback.
 void ReportLanguageDetectionError();
 
 void ReportLocalesOnDisabledByPrefs(const std::string& locale);
 
 // Called when Chrome Translate server sends the language list which includes
 // a undisplayable language in the user's locale.
 void ReportUndisplayableLanguage(const std::string& language);
 
 void ReportUnsupportedLanguageAtInitiation(const std::string& language);
 
 // Provides UMA entry names for unit tests.
 const char* GetMetricsName(MetricsNameIndex index);
 
 }  // namespace TranslateBrowserMetrics
 
 #endif  // CHROME_BROWSER_TRANSLATE_TRANSLATE_BROWSER_METRICS_H_