Address more TODO(GYP) in the GN build.

components/crash/content/app/BUILD.gn

 # 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.
 
+assert(!is_ios)
 if (is_android) {
   import("//build/config/android/config.gni")
 }
 
 source_set("lib") {
   sources = [
     "crash_keys_win.cc",
     "crash_keys_win.h",
     "crash_reporter_client.cc",
     "crash_reporter_client.h",
@@ skipping 165 matching lines @@
     if (is_mac) {
       deps += [ "//breakpad" ]
     }
 
     if (is_win) {
       deps += [ "//breakpad:breakpad_handler" ]
       libs = [ "userenv.lib" ]
     }
   }
 }
+
+if (is_mac) {
+  source_set("breakpad_stubs") {
+    sources = [
+      "breakpad_mac.h",
+      "breakpad_mac_stubs.mm",
+      "crash_reporter_client.cc",
+      "crash_reporter_client.h",
+    ]
+    deps = [
+      "//base",
+    ]
+  }
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "crash_keys_win_unittest.cc",
+  ]
+  deps = [
+    ":lib",
+    "//base",
+    "//testing/gmock",
+    "//testing/gtest",
+  ]
+
+  if (is_win) {
+    deps += [ "//breakpad:client" ]
+  }
+}