Don't download identical APKs on update.

chrome/browser/android/webapk/webapk_installer_unittest.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 <jni.h>
 #include <memory>
 #include <string>
 
@@ skipping 403 matching lines @@
   EXPECT_FALSE(runner->success());
 }
 
 // Test update succeeding.
 TEST_F(WebApkInstallerTest, UpdateSuccess) {
   std::unique_ptr<WebApkInstallerRunner> runner = CreateWebApkInstallerRunner();
   runner->RunUpdateWebApk();
   EXPECT_TRUE(runner->success());
 }
 
+// Test that an update suceeds if the WebAPK server returns a HTTP response with
+// an empty download URL. The WebAPK server sends an empty download URL when:
+// - The server is unable to update the WebAPK in the way that the client
+//   requested.
+// AND
+// - The most up to date version of the WebAPK on the server is identical to the
+//   one installed on the client.
+TEST_F(WebApkInstallerTest, UpdateSuccessWithEmptyDownloadUrlInResponse) {
+  SetWebApkResponseBuilder(base::Bind(&BuildValidWebApkResponse, GURL()));
+
+  std::unique_ptr<WebApkInstallerRunner> runner = CreateWebApkInstallerRunner();
+  runner->RunUpdateWebApk();
+  EXPECT_TRUE(runner->success());
+}
+
 // Test installation succeeds using Google Play.
 TEST_F(WebApkInstallerTest, InstallFromGooglePlaySuccess) {
   std::unique_ptr<WebApkInstallerRunner> runner = CreateWebApkInstallerRunner();
   runner->SetCanUseGooglePlayInstallService(true);
   runner->RunInstallWebApk();
   EXPECT_TRUE(runner->success());
 }
 
 // When there is no Web Manifest available for a site, an empty
 // |best_primary_icon_url| is used to build a WebApk update request. Tests the
@@ skipping 59 matching lines @@
     icons[i] = manifest.icons(i);
 
   EXPECT_EQ(best_primary_icon_url.spec(), icons[0].src());
   EXPECT_EQ(best_primary_icon_murmur2_hash, icons[0].hash());
   EXPECT_TRUE(icons[0].has_image_data());
 
   EXPECT_EQ(icon_url_1.spec(), icons[1].src());
   EXPECT_EQ(icon_murmur2_hash_1, icons[1].hash());
   EXPECT_FALSE(icons[1].has_image_data());
 }