Add WebAPK installation metrics.

chrome/browser/android/webapk/webapk_metrics.cc

+// 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.
+
+#include "chrome/browser/android/webapk/webapk_metrics.h"
+
+#include "base/metrics/histogram_macros.h"
+
+namespace webapk {
+
+const char kInstallEventHistogram[] = "WebApk.Install.InstallEvent";
+const char kStartTypeHistogram[] = "WebApk.Install.StartType";
+const char kUserActionHistogram[] = "WebApk.Install.UserAction";
+
+void TrackInstallEvent(InstallEvent event) {
+  UMA_HISTOGRAM_ENUMERATION(kInstallEventHistogram, event, INSTALL_EVENT_MAX);
+}
+
+void TrackStartType(StartType event) {
+  UMA_HISTOGRAM_ENUMERATION(kStartTypeHistogram, event, START_TYPE_MAX);
+}
+
+void TrackUserAction(UserAction event) {
+  UMA_HISTOGRAM_ENUMERATION(kUserActionHistogram, event, USER_ACTION_MAX);
+}
+
+}  // namespace webapk