Split the NOT_STARTED and STOPPED_BEFORE_COMPLETION installability metrics.

chrome/browser/installable/installable_metrics.h

 // Copyright 2017 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_INSTALLABLE_INSTALLABLE_METRICS_H_
 #define CHROME_BROWSER_INSTALLABLE_INSTALLABLE_METRICS_H_
 
 // This enum backs a UMA histogram and must be treated as append-only.
 enum class InstallabilityCheckStatus {
   NOT_STARTED,
-  STOPPED_BEFORE_COMPLETION,
+  NOT_COMPLETED,
   IN_PROGRESS_NON_PROGRESSIVE_WEB_APP,
   IN_PROGRESS_PROGRESSIVE_WEB_APP,
   COMPLETE_NON_PROGRESSIVE_WEB_APP,
   COMPLETE_PROGRESSIVE_WEB_APP,
   COUNT,
 };
 
 class InstallableMetrics {
  public:
   static void RecordMenuOpenHistogram(InstallabilityCheckStatus status);
   static void RecordMenuItemAddToHomescreenHistogram(
       InstallabilityCheckStatus status);
 };
 
 #endif  // CHROME_BROWSER_INSTALLABLE_INSTALLABLE_METRICS_H_