Chrome talks to Play to install WebAPKs.

chrome/android/java_sources.gni

 # 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.
 
 chrome_java_sources = [
   "java/src/com/google/android/apps/chrome/appwidget/bookmarks/BookmarkThumbnailWidgetProvider.java",
   "java/src/org/chromium/chrome/browser/ActivityTabTaskDescriptionHelper.java",
   "java/src/org/chromium/chrome/browser/ActivityTaskDescriptionIconGenerator.java",
   "java/src/org/chromium/chrome/browser/AfterStartupTaskUtils.java",
   "java/src/org/chromium/chrome/browser/ApplicationInitialization.java",
@@ skipping 1013 matching lines @@
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity2.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity3.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity4.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity5.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity6.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity7.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity8.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity9.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkInfo.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkInstaller.java",
+  "java/src/org/chromium/chrome/browser/webapps/WebApkInstallClientDelegate.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkManagedActivity.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkUpdateManager.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkVersionManager.java",
   "java/src/org/chromium/chrome/browser/webapps/WebappActivity.java",
   "java/src/org/chromium/chrome/browser/webapps/WebappActivity0.java",
   "java/src/org/chromium/chrome/browser/webapps/WebappActivity1.java",
   "java/src/org/chromium/chrome/browser/webapps/WebappActivity2.java",
   "java/src/org/chromium/chrome/browser/webapps/WebappActivity3.java",
   "java/src/org/chromium/chrome/browser/webapps/WebappActivity4.java",
   "java/src/org/chromium/chrome/browser/webapps/WebappActivity5.java",
@@ skipping 479 matching lines @@
   "sync_shell/javatests/src/org/chromium/chrome/browser/sync/SyncTestBase.java",
   "sync_shell/javatests/src/org/chromium/chrome/browser/sync/TypedUrlsTest.java",
   "sync_shell/javatests/src/org/chromium/chrome/browser/sync/ui/PassphraseTypeDialogFragmentTest.java",
 ]
 
 # Only used for testing, should not be shipped to end users.
 if (!is_official_build) {
   chrome_java_sources += [ "java/src/org/chromium/chrome/browser/offlinepages/evaluation/OfflinePageEvaluationBridge.java" ]
   chrome_test_java_sources += [ "javatests/src/org/chromium/chrome/browser/offlinepages/OfflinePageSavePageLaterEvaluationTest.java" ]
 }