Port custom_tabs_client from GYP to GN

build/config/android/internal_rules.gni

 # 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/zip.gni")
 import("//third_party/ijar/ijar.gni")
 
 assert(is_android)
 
@@ skipping 1174 matching lines @@
   _final_datadeps = []
   if (defined(invoker.datadeps)) {
     _final_datadeps = invoker.datadeps
   }
 
   _supports_android =
       defined(invoker.supports_android) && invoker.supports_android
   _requires_android =
       defined(invoker.requires_android) && invoker.requires_android
   assert(_requires_android || true)  # Mark as used.
+  _android_manifest = "//build/android/AndroidManifest.xml"
+  if (defined(invoker.android_manifest)) {
+    _android_manifest = invoker.android_manifest
+  }
+  assert(_android_manifest != "")  # Mark as used.
   _run_findbugs = defined(invoker.run_findbugs) && invoker.run_findbugs
   assert(_run_findbugs || true)  # Mark as used.
 
   if (_supports_android) {
     _dex_path = _base_path + ".dex.jar"
     if (defined(invoker.dex_path)) {
       _dex_path = invoker.dex_path
     }
   }
 
@@ skipping 104 matching lines @@
                              ])
       build_config = _build_config
       jar_path = _jar_path
       script_name = _template_name
       deps = build_config_deps
     }
   }
 
   if (_supports_android) {
     if (defined(invoker.chromium_code) && invoker.chromium_code) {
-      _android_manifest = "//build/android/AndroidManifest.xml"
-      if (defined(invoker.android_manifest)) {
-        _android_manifest = invoker.android_manifest
-      }
-
       _final_datadeps += [ ":${_template_name}__lint" ]
       android_lint("${_template_name}__lint") {
         android_manifest = _android_manifest
         jar_path = _jar_path
         java_files = _java_files
         deps = [
           ":$_compile_java_target",
         ]
         if (defined(invoker.deps)) {
           deps += invoker.deps
@@ skipping 310 matching lines @@
     ]
     args = [
       "--depfile",
       rebase_path(depfile, root_build_dir),
       "--script-output-path",
       rebase_path(generated_script, root_build_dir),
     ]
     args += test_runner_args
   }
 }