Record UMA in ArcNavigationThrottle::OnDisambigDialogClosed

chrome/browser/chromeos/arc/arc_navigation_throttle.h

 // Copyright 2016 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_CHROMEOS_ARC_ARC_NAVIGATION_THROTTLE_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_ARC_NAVIGATION_THROTTLE_H_
 
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "components/arc/intent_helper/activity_icon_loader.h"
 #include "content/public/browser/navigation_throttle.h"
 #include "ui/gfx/image/image.h"
 
 namespace content {
 class NavigationHandle;
 }  // namespace content
 
 namespace arc {
 
 // A class that allow us to retrieve ARC app's information and handle URL
 // traffic initiated on Chrome browser, either on Chrome or an ARC's app.
 class ArcNavigationThrottle : public content::NavigationThrottle {
  public:
-  enum class CloseReason {
-    REASON_ALWAYS_PRESSED,
-    REASON_JUST_ONCE_PRESSED,
-    REASON_DIALOG_DEACTIVATED,
-    REASON_PREFERRED_ACTIVITY_FOUND,
-    REASON_ERROR
+  // These enums are used to define the buckets for an enumerated UMA histogram
+  // and need to be synced with histograms.xml. This enum class should also be
+  // treated as append-only.
+  enum class CloseReason : int {
+    ERROR = 0,
+    DIALOG_DEACTIVATED = 1,
+    ALWAYS_PRESSED = 2,
+    JUST_ONCE_PRESSED = 3,
+    PREFERRED_ACTIVITY_FOUND = 4,
+    SIZE,
   };
 
   using NameAndIcon = std::pair<std::string, gfx::Image>;
   using ShowDisambigDialogCallback =
       base::Callback<void(content::NavigationHandle* handle,
                           const std::vector<NameAndIcon>& app_info,
                           const base::Callback<void(size_t, CloseReason)>& cb)>;
   ArcNavigationThrottle(
       content::NavigationHandle* navigation_handle,
       const ShowDisambigDialogCallback& show_disambig_dialog_cb);
@@ skipping 18 matching lines @@
   ShowDisambigDialogCallback show_disambig_dialog_callback_;
 
   base::WeakPtrFactory<ArcNavigationThrottle> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcNavigationThrottle);
 };
 
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_ARC_NAVIGATION_THROTTLE_H_