Add metrics for webapk update rate.

chrome/android/java/src/org/chromium/chrome/browser/metrics/WebApkUma.java

 // Copyright 2017 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.
 
 package org.chromium.chrome.browser.metrics;
 
 import org.chromium.base.metrics.RecordHistogram;
 
 import java.util.concurrent.TimeUnit;
 
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     /**
      * Records whether installing a WebAPK from Google Play succeeded. If not, records the reason
      * that the install failed.
      */
     public static void recordGooglePlayInstallResult(int result) {
         assert result >= 0 && result < GOOGLE_PLAY_INSTALL_RESULT_MAX;
         RecordHistogram.recordEnumeratedHistogram(
                 "WebApk.Install.GooglePlayInstallResult", result, GOOGLE_PLAY_INSTALL_RESULT_MAX);
     }
 
+    /**
+     * Records whether updating a WebAPK from Google Play succeeded. If not, records the reason
+     * that the update failed.
+     */
+    public static void recordGooglePlayUpdateResult(int result) {
+        assert result >= 0 && result < GOOGLE_PLAY_INSTALL_RESULT_MAX;
+        RecordHistogram.recordEnumeratedHistogram(
+                "WebApk.Update.GooglePlayUpdateResult", result, GOOGLE_PLAY_INSTALL_RESULT_MAX);
+    }
+
     /** Records the duration of a WebAPK session (from launch/foreground to background). */
     public static void recordWebApkSessionDuration(long duration) {
         RecordHistogram.recordLongTimesHistogram(
                 "WebApk.Session.TotalDuration", duration, TimeUnit.MILLISECONDS);
     }
 }