Record UMA in ArcNavigationThrottle::OnDisambigDialogClosed

chrome/browser/chromeos/arc/arc_navigation_throttle.h

Index: chrome/browser/chromeos/arc/arc_navigation_throttle.h
diff --git a/chrome/browser/chromeos/arc/arc_navigation_throttle.h b/chrome/browser/chromeos/arc/arc_navigation_throttle.h
index c385b979c33bcc6ef2b87162d972d2c65e84eb97..95d377f12e45d8bdd43c22799abf136482bdf363 100644
--- a/chrome/browser/chromeos/arc/arc_navigation_throttle.h
+++ b/chrome/browser/chromeos/arc/arc_navigation_throttle.h
@@ -26,12 +26,15 @@ namespace arc {
 // 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.

[Ilya Sherman, 2016/06/28 03:17:15]

nit: Please also document that this enum should be treated as append-only.

[Yusuke Sato, 2016/06/28 05:04:23]

Done.

+  enum class CloseReason : int {
+    REASON_ALWAYS_PRESSED = 0,
+    REASON_JUST_ONCE_PRESSED = 1,
+    REASON_PREFERRED_ACTIVITY_FOUND = 2,
+    REASON_DIALOG_DEACTIVATED = 3,
+    REASON_ERROR = 4,

[Ilya Sherman, 2016/06/28 03:17:15]

Optional nit: I'd omit the "REASON_" prefix since this is an enum class.

[Yusuke Sato, 2016/06/28 05:04:23]

Done.

+    SIZE,
   };
 
   using NameAndIcon = std::pair<std::string, gfx::Image>;