Add a chrome://webapks page.

components/webapks_ui/webapks_ui_constants.cc

Index: components/webapks_ui/webapks_ui_constants.cc
diff --git a/components/webapks_ui/webapks_ui_constants.cc b/components/webapks_ui/webapks_ui_constants.cc
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+++ b/components/webapks_ui/webapks_ui_constants.cc
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+// Copyright 2017 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 "components/webapks_ui/webapks_ui_constants.h"
+
+namespace webapks_ui {
+
+// Resource paths.
+const char kAboutWebApksCSS[] = "about_webapks.css";
+const char kWebApksJS[] = "webapks.js";
+
+// Message handlers.
+const char kRequestWebApksInfo[] = "requestWebApksInfo";
+const char kReturnWebApksInfo[] = "returnWebApksInfo";
+
+// Strings.
+const char kTitle[] = "title";
+const char kHeader[] = "header";
+const char kPackageName[] = "packageName";
+const char kShellApkVersion[] = "shellApkVersion";
+const char kVersionCode[] = "versionCode";
+
+}  // namespace webapks_ui