Add WebAPK installation metrics.

chrome/browser/android/webapk/webapk_metrics.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_ANDROID_WEBAPK_WEBAPK_METRICS_H_
+#define CHROME_BROWSER_ANDROID_WEBAPK_WEBAPK_METRICS_H_
+
+#include "base/macros.h"
+
+namespace webapk {
+
+// This enum backs a UMA histogram, so it should be treated as append-only.
+enum InstallEvent {
+  INSTALL_EVENT_MIN = 0,
+  INSTALL_EVENT_ADD_FROM_BANNER_STARTED = 1,
+  INSTALL_EVENT_ADD_FROM_MENU_STARTED = 2,
+  INSTALL_EVENT_COMPLETED = 3,
+  INSTALL_EVENT_FAILED = 4,
+  INSTALL_EVENT_MAX = 5,
+};
+
+// This enum backs a UMA histogram, so it should be treated as append-only.
+enum DismissEvent {
+  DISMISS_EVENT_MIN = 10,

[dominickn, 2016/09/05 07:34:31]

Start these enums from 0. The app banner ones don't for historical reasons; if I
was reimplementing them (which I will be), I'm going to start them all from 0.

Additionally, you should do:

enum InstallEvent {
   INSTALL_EVENT_MIN = 0,
   INSTALL_EVENT_ADD_FROM_BANNER_STARTED = INSTALL_EVENT_MIN,
   //etc.
}

So that we don't waste the 0 bucket.

[Xi Han, 2016/09/07 20:58:52]

I see, thanks, updated. Also, since I changed to UMA_HISTOGRAM_ENUMRATION, the
declaration of the event enum is more flexible. 

+  DISMISS_EVENT_ADD_TO_HOMESCREEN = 11,
+  DISMISS_EVENT_ADDING = 12,
+  DISMISS_EVENT_OPEN = 13,
+  DISMISS_EVENT_MAX = 14,
+};
+
+// This enum backs a UMA histogram, so it should be treated as append-only.
+enum UserAction {
+  USER_ACTION_MIN = 20,
+  USER_ACTION_ADD_FROM_MENU = 21,
+  USER_ACTION_ADD_FROM_BANNER_ACCEPTED = 22,
+  USER_ACTION_INSTALLED_OPEN = 23,
+  // Banner is deleted due to the fact that user closes the associated tab
+  // or Chrome. The cases that user closes the banner (clicks
+  // the "X" button) are recorded in the |DissmissEvent|.
+  USER_ACTION_BANNER_IGNORED = 24,
+  USER_ACTION_MAX = 25,
+};
+
+extern const char kDismissEventHistogram[];
+extern const char kInstallEventHistogram[];
+extern const char kUserActionHistogram[];
+
+void TrackDismissEvent(int event);
+void TrackInstallEvent(int event);
+void TrackUserAction(int event);
+
+};  // namespace webapk
+
+#endif  // CHROME_BROWSER_ANDROID_WEBAPK_WEBAPK_METRICS_H_