Allow overridding "app_name" for "test" template on iOS.

testing/test.gni

 # Copyright 2015 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.
 
 # ==============================================================================
 # TEST SETUP
 # ==============================================================================
 
 template("_gen_isolate") {
   testonly = true
@@ skipping 277 matching lines @@
       ]
       outputs = [
         "{{bundle_resources_dir}}/{{source_file_part}}",
       ]
     }
 
     ios_app_bundle(_test_target) {
       # TODO: Make this configurable and only provide a default that can be
       # overridden.
       info_plist = "//testing/gtest_ios/unittest-Info.plist"
-      app_name = target_name
       entitlements_path = "//testing/gtest_ios"
       code_signing_identity = ""
       testonly = true
+
+      # TODO(crbug.com/603102): remove this once gyp support is dropped and all
+      # application uses the target name as value for BUNDLE_ID_TEST_NAME.
+      if (defined(invoker.app_name)) {
+        app_name = invoker.app_name
+      } else {
+        app_name = target_name
+      }
+
       extra_substitutions = [ "BUNDLE_ID_TEST_NAME=$app_name" ]
 
       # See above call.
       set_sources_assignment_filter([])
 
       forward_variables_from(invoker, "*")
 
       if (!defined(deps)) {
         deps = []
       }
@@ skipping 33 matching lines @@
     if (defined(invoker.output_name) && target_name != invoker.output_name) {
       group("${invoker.output_name}_run") {
         testonly = true
         deps = [
           ":${invoker.target_name}",
         ]
       }
     }
   }
 }