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_
+
+namespace webapk {
+
+// Keep these enums up to date with tools/metrics/histograms/histograms.xml.
+// Events for WebAPKs installation flow. The sum of |InstalllEvent| histogram
+// is the total number of times that a WebAPK infobar was triggered.
+enum InstallEvent {
+  // The user did not interact with the banner.
+  BANNER_IGNORED,
+  // The banner with the "Add-to-Homescreen" button is dismissed before the
+  // installation started. "Dismiss" means the user closes the banner by
+  // clicking the "X" button.
+  BANNER_DISMISSED_BEFORE_INSTALLATION,
+  // The banner with the "Adding" button is dismissed during installation.
+  BANNER_DISMISSED_DURING_INSTALLATION,
+  INSTALL_COMPLETED,
+  INSTALL_FAILED,
+  INSTALL_EVENT_MAX,
+};
+
+// The ways in which WebAPK instllation can be started.

[dominickn, 2016/09/21 06:54:27]

Nit: "installation"

[Xi Han, 2016/09/21 14:22:08]

Sorry for the typo.

+enum InstallStartType {
+  STARTED_FROM_BANNER,
+  STARTED_FROM_ADD_TO_HOME_SCREEN_MENU,

[dominickn, 2016/09/21 06:54:28]

General nit: change ADD_TO_HOME_SCREEN_MENU to just MENU in these, that's much
easier to parse.

[Xi Han, 2016/09/21 14:22:08]

Done.

+  START_TYPE_MAX,
+};
+
+// The ways in which WebApk installation can be triggered.

[dominickn, 2016/09/21 06:54:28]

Splitting these histograms is the right move, but I still think the distinction
between "triggered" and "started" is very easy to get wrong. How about this:

// The WebAPK infobar source, i.e. where the infobar was triggered from.
enum InfoBarShown {
  WEBAPK_INFOBAR_SHOWN_FROM_MENU,
  WEBAPK_INFOBAR_SHOWN_FROM_BANNER,
  WEBAPK_INFOBAR_SHOWN_MAX
}

// The WebAPK installation source, i.e. where an installation was triggered
from. Counts under INSTALL_SOURCE_MENU should be identical to
WEBAPK_INFOBAR_SHOWN_FROM_MENU, as the add to homescreen menu item immediately
shows the WebAPK infobar and starts the installation. Counts under
INSTALL_SOURCE_BANNER will be lower than WEBAPK_INFOBAR_SHOWN_BANNER, as users
must explicitly click accept in the infobar to begin the installation from a
banner.
enum InstallSource {
  INSTALL_SOURCE_BANNER,
  INSTALL_SOURCE_MENU,
  INSTALL_SOURCE_MAX
}

This is much clearer to me that one is about when a WebAPK infobar is shown, and
the other is when WebAPK installation starts. If you try and remove usage of the
"banner" term, and instead use "WebAPK infobar" in comments where you could have
the A2HS menu item or app banners triggering the infobar, I think that will help
too. Thoughts?

Btw, sorry it's taken me this long to think about the naming. The metrics here
are quite complicated, and I think that getting the names right is really
important to make sure that we can interpret everything.

[Xi Han, 2016/09/21 14:22:08]

That is correct.
Agree, infobar is preferred here, comparing with app banners. I will update
comments.

 
Totally agree.

+enum InstallTriggeredType {
+  TRIGGERED_FROM_BANNER,
+  TRIGGERED_FROM_ADD_TO_HOME_SCREEN_MENU,
+  TRIGGERED_TYPE_MAX,
+};
+
+// User actions after a WebAPK is installed.
+enum UserAction {
+  // TODO(hanxi|zpeng): Records the first two user actions after
+  // crbug.com/638614 is fixed.
+  // Launch a previously installed WebAPK since the WebAPK has been installed on
+  // the device before.
+  USER_ACTION_OPEN,
+  USER_ACTION_OPEN_DISMISS,
+  // Open a newly installed WebAPK via a successful installation.
+  USER_ACTION_INSTALLED_OPEN,
+  USER_ACTION_INSTALLED_OPEN_DISMISS,
+  USER_ACTION_MAX,
+};
+
+void TrackInstallEvent(InstallEvent event);
+void TrackInstallStartType(InstallStartType event);
+void TrackInstallTriggeredType(InstallTriggeredType event);
+void TrackUserAction(UserAction event);
+
+};  // namespace webapk
+
+#endif  // CHROME_BROWSER_ANDROID_WEBAPK_WEBAPK_METRICS_H_