Fix DCHECK failure and add unittest for BlimpSystemURLContextGetter.

blimp/engine/BUILD.gn

 # 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.
 
 import("//build/config/features.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//tools/grit/repack.gni")
 import("//tools/grit/grit_rule.gni")
@@ skipping 316 matching lines @@
     ":app",
     "//base",
   ]
 }
 
 source_set("app_unit_tests") {
   testonly = true
 
   sources = [
     "app/blimp_engine_config_unittest.cc",
+    "app/blimp_system_url_request_context_getter_unittest.cc",
     "app/settings_manager_unittest.cc",
     "app/ui/blimp_screen_unittest.cc",
   ]
 
   deps = [
     ":app",
     ":app_config",
+    ":app_net",
     ":app_settings",
     ":app_switches",
     "//base",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
     "//blimp/engine:app_ui",
+    "//content/test:test_support",
     "//testing/gmock",
     "//testing/gtest",
     "//ui/display",
     "//ui/gfx:test_support",
   ]
 }
 
 source_set("feature_unit_tests") {
   testonly = true
 
@@ skipping 102 matching lines @@
       _rebased_dockerfile,
       "--startup-script",
       _rebased_startup_script,
       "--manifest",
       _rebased_manifest,
       "--output",
       rebase_path(_bundle),
     ]
   }
 }