app_shell: Add version number in user agent

Some sites sniff the Chrome version number, so app_shell needs to
provide one.

BUG=407236
TEST=app_shell_unittests ShellContentClientTest.UserAgentFormat

Review URL: https://codereview.chromium.org/505403003

Cr-Commit-Position: refs/heads/master@{#292063}

extensions/shell/app_shell.gyp

@@ -204,6 +204,7 @@
         '../test/extensions_unittests_main.cc',
         'browser/shell_desktop_controller_unittest.cc',
         'browser/shell_nacl_browser_delegate_unittest.cc',
+        'common/shell_content_client_unittest.cc'
       ],
       'conditions': [
         ['disable_nacl==1', {

extensions/shell/common/shell_content_client.cc

@@ -8,6 +8,7 @@
 #include "base/strings/utf_string_conversions.h"
 #include "content/public/common/user_agent.h"
 #include "extensions/common/constants.h"
+#include "extensions/shell/common/version.h"  // Generated file.
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 
@@ -83,9 +84,9 @@ void ShellContentClient::AddAdditionalSchemes(
 }
 
 std::string ShellContentClient::GetUserAgent() const {
-  // TODO(derat): Figure out what this should be for app_shell and determine
-  // whether we need to include a version number to placate browser sniffing.
-  return content::BuildUserAgentFromProduct("Chrome");
+  // Must contain a user agent string for version sniffing. For example,
+  // pluginless WebRTC Hangouts checks the Chrome version number.
+  return content::BuildUserAgentFromProduct("Chrome/" PRODUCT_VERSION);
 }
 
 base::string16 ShellContentClient::GetLocalizedString(int message_id) const {

extensions/shell/common/shell_content_client_unittest.cc

+// Copyright 2014 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 "extensions/shell/common/shell_content_client.h"
+
+#include <string>
+
+#include "base/strings/string_util.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+typedef testing::Test ShellContentClientTest;
+
+namespace extensions {
+
+// Tests that the app_shell user agent looks like a Chrome user agent.
+TEST_F(ShellContentClientTest, UserAgentFormat) {
+  ShellContentClient client;
+  std::string user_agent = client.GetUserAgent();
+
+  // Must start with the usual Mozilla-compatibility string.
+  EXPECT_TRUE(StartsWithASCII(user_agent, "Mozilla/5.0", false)) << user_agent;
+
+  // Must contain a substring like "Chrome/1.2.3.4".
+  EXPECT_TRUE(MatchPattern(user_agent, "*Chrome/*.*.*.*")) << user_agent;
+}
+
+}  // namespace extensions