Make sure custom proxy config is always a valid pointer

This was part of the reason one of the Android tests is failing.

Bug: 721403
Change-Id: I58493a24c32aaac2e568ade3541dea36ff87b88c
Reviewed-on: https://chromium-review.googlesource.com/c/1352325Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611496}

services/network/network_service_proxy_delegate.cc

@@ -102,7 +102,12 @@ NetworkServiceProxyDelegate::NetworkServiceProxyDelegate(
     mojom::CustomProxyConfigClientRequest config_client_request)
     : proxy_config_(std::move(initial_config)),
       binding_(this, std::move(config_client_request)),
-      should_use_alternate_proxy_list_cache_(kMaxCacheSize) {}
+      should_use_alternate_proxy_list_cache_(kMaxCacheSize) {
+  // Make sure there is always a valid proxy config so we don't need to null
+  // check it.
+  if (!proxy_config_)
+    proxy_config_ = mojom::CustomProxyConfig::New();
+}
 
 void NetworkServiceProxyDelegate::OnBeforeStartTransaction(
     net::URLRequest* request,

services/network/network_service_proxy_delegate_unittest.cc

@@ -50,6 +50,16 @@ class NetworkServiceProxyDelegateTest : public testing::Test {
   base::test::ScopedTaskEnvironment scoped_task_environment_;
 };
 
+TEST_F(NetworkServiceProxyDelegateTest, NullConfigDoesNotCrash) {
+  mojom::CustomProxyConfigClientPtr client;
+  auto delegate = std::make_unique<NetworkServiceProxyDelegate>(
+      nullptr, mojo::MakeRequest(&client));
+
+  net::HttpRequestHeaders headers;
+  auto request = CreateRequest(GURL(kHttpUrl));
+  delegate->OnBeforeStartTransaction(request.get(), &headers);
+}
+
 TEST_F(NetworkServiceProxyDelegateTest, AddsHeadersBeforeCache) {
   auto config = mojom::CustomProxyConfig::New();
   config->rules.ParseFromString("http=proxy");