Don't download identical APKs on update.

chrome/browser/android/webapk/webapk_installer.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_installer.h"
 
 #include "base/android/build_info.h"
 #include "base/android/jni_android.h"
 #include "base/android/jni_string.h"
 #include "base/android/path_utils.h"
@@ skipping 400 matching lines @@
   source->GetResponseAsString(&response_string);
 
   std::unique_ptr<webapk::WebApkResponse> response(
       new webapk::WebApkResponse);
   if (!response->ParseFromString(response_string)) {
     OnFailure();
     return;
   }
 
   GURL signed_download_url(response->signed_download_url());
+  // https://crbug.com/680131. The server sends an empty URL if the server does
+  // not have a newer WebAPK to update to.
+  if (task_type_ == UPDATE && signed_download_url.is_empty()) {
+    OnSuccess();
+    return;
+  }
+
   if (!signed_download_url.is_valid() || response->package_name().empty()) {
     OnFailure();
     return;
   }
 
   if (HasGooglePlayWebApkInstallDelegate()) {
     int version = 1;
     base::StringToInt(response->version(), &version);
     if (!InstallOrUpdateWebApkFromGooglePlay(
         response->package_name(), version, response->token())) {
@@ skipping 184 matching lines @@
 
 void WebApkInstaller::OnSuccess() {
   finish_callback_.Run(true, webapk_package_);
   delete this;
 }
 
 void WebApkInstaller::OnFailure() {
   finish_callback_.Run(false, webapk_package_);
   delete this;
 }