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"

[dominickn, 2016/09/09 08:14:11]

Nit: I don't think you use this header.

[Xi Han, 2016/09/09 15:37:32]

Done.

+
+namespace webapk {
+
+// The states of WebAPK installation process. These states are tracked to
+// record dismiss events for WebAPK installation.
+enum InstallState {

[dominickn, 2016/09/09 08:14:12]

Nit: histograms reviewer will probably ask you to add this comment to all of
these enums.

"This enum backs an UMA histogram, and new entries must be added at the end
prior to INSTALL_EVENT_MAX"

[dominickn, 2016/09/09 08:14:12]

This is actually a DismissEvent enum - it's recording what state the WebAPK
installation was in when the infobar was dismissed. Rename it, e.g.
InstallStateOnDismiss.

[Xi Han, 2016/09/09 15:37:32]

Updated.
 
The InstallState isn't for a UMA histogram, so I think maybe it is better to
move it back to AppBannerInfobarDelegateAndroid to avoid confusion? Besides, do
we really need to rename it to InstallStateOnDismiss since these states are
fairly generic?

+  WAIT_FOR_START,
+  INSTALLING,
+  INSTALLED,
+};
+
+// Keep these enums up to date with tools/metrics/histograms/histograms.xml.
+// The sum of |InstalllEvent| histogram is the total number of times that a
+// WebAPK infobar was triggered.
+enum InstallEvent {
+  // Banner is deleted due to the closing of Chrome or the associated tab.
+  INSTALL_EVENT_BANNER_IGNORED = 0,

[dominickn, 2016/09/09 08:14:12]

Nit: I don't think you need the explicit = 0 now.

[Xi Han, 2016/09/09 15:37:32]

Done.

+  // The banner with the "Add-to-Homescreen" button is dismissed before the
+  // installation stared. The *_DISMISS events are the cases that user

[dominickn, 2016/09/09 08:14:12]

Nit: installation started

Nit: that the user

Nit: no more _DISMISS events

[Xi Han, 2016/09/09 15:37:32]

Updated to: "Dismiss" means the user closes the banner by clicking the "X"
button."
Is this one better?

+  // closes the banner by clicking the "X" button.
+  INSTALL_EVENT_ADD_TO_HOME_SCREEN_DISMISS,
+  // The banner with the "Adding" button is dismissed during installation.
+  INSTALL_EVENT_ADDING_DISMISS,
+  INSTALL_EVENT_COMPLETED,
+  INSTALL_EVENT_FAILED,
+  INSTALL_EVENT_MAX,
+};
+
+enum StartType {
+  TRIGGERED_FROM_BANNER = 0,
+  STARTED_FROM_BANNER,
+  STARTED_FROM_ADD_TO_HOME_SCREEN_MENU,
+  START_TYPE_MAX,
+};
+
+enum UserAction {
+  USER_ACTION_INSTALLED_OPEN = 0,
+  USER_ACTION_INSTALLED_OPEN_DISMISS,
+  USER_ACTION_MAX,
+};
+
+void TrackInstallEvent(InstallEvent event);
+void TrackStartType(StartType event);
+void TrackUserAction(UserAction event);
+
+};  // namespace webapk
+
+#endif  // CHROME_BROWSER_ANDROID_WEBAPK_WEBAPK_METRICS_H_