[Cronet] Make cronet_tests run in Linux Release config.

- Add libcronet.so to cronet_tests rpath.
- Use trivial ProxyResolutionService to avoid crashes.

Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I3a114b098a4d78e4087be948dfd3ce303d6df737
Bug: 813226
Reviewed-on: https://chromium-review.googlesource.com/987521Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Misha Efimov <mef@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547521}

components/cronet/BUILD.gn

@@ -98,6 +98,10 @@ if (!is_ios && !is_android) {
     sources = [
       "run_all_unittests.cc",
     ]
+
+    if (is_linux && !is_component_build) {
+      public_configs = [ "//build/config/gcc:rpath_for_built_shared_libraries" ]
+    }
   }
 
   test("cronet_unittests") {

components/cronet/cronet_global_state_stubs.cc

@@ -57,17 +57,15 @@ void PostTaskToInitThread(const base::Location& posted_from,
 
 std::unique_ptr<net::ProxyConfigService> CreateProxyConfigService(
     const scoped_refptr<base::SequencedTaskRunner>& io_task_runner) {
-  // TODO(https://crbug.com/813226): Add ProxyConfigService support.
-  NOTIMPLEMENTED();
-  return nullptr;
+  return net::ProxyResolutionService::CreateSystemProxyConfigService(
+      io_task_runner);
 }
 
 std::unique_ptr<net::ProxyResolutionService> CreateProxyResolutionService(
     std::unique_ptr<net::ProxyConfigService> proxy_config_service,
     net::NetLog* net_log) {
-  // TODO(https://crbug.com/813226): Add ProxyResolutionService support.
-  NOTIMPLEMENTED();
-  return nullptr;
+  return net::ProxyResolutionService::CreateUsingSystemProxyResolver(
+      std::move(proxy_config_service), net_log);
 }
 
 std::string CreateDefaultUserAgent(const std::string& partial_user_agent) {