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/vr_shell/VrCoreVersionChecker.java",
   "java/src/org/chromium/chrome/browser/vr_shell/VrDaydreamApi.java",
   "java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java",
   "java/src/org/chromium/chrome/browser/vr_shell/VrShell.java",
   "java/src/org/chromium/chrome/browser/webapps/ActivityAssigner.java",
   "java/src/org/chromium/chrome/browser/webapps/AddToHomescreenDialog.java",
   "java/src/org/chromium/chrome/browser/webapps/AddToHomescreenManager.java",
   "java/src/org/chromium/chrome/browser/webapps/ChromeWebApkHost.java",
   "java/src/org/chromium/chrome/browser/webapps/FullScreenActivity.java",
   "java/src/org/chromium/chrome/browser/webapps/FullScreenDelegateFactory.java",
+  "java/src/org/chromium/chrome/browser/webapps/GooglePlayWebApkInstallDelegate.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity0.java",
   "java/src/org/chromium/chrome/browser/webapps/WebApkActivity1.java",
   "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",
@@ skipping 495 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" ]
 }