Replace two references to io_task_runner in net's proxy config code.

The system ProxyConfigService is now created on Chrome's UI thread, so
the references were outdated.  Also, net/ really shouldn't know about
content/'s threads.

Bug: 823063
Change-Id: I399bdc13fa46b89f45111cafb393e2c9cd735bdd
Reviewed-on: https://chromium-review.googlesource.com/978386
Commit-Queue: Eric Roman <eroman@chromium.org>
Reviewed-by: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545614}

net/proxy_resolution/proxy_config_service_linux.h

@@ -299,9 +299,9 @@ class NET_EXPORT_PRIVATE ProxyConfigServiceLinux : public ProxyConfigService {
 
   void SetupAndFetchInitialConfig(
       const scoped_refptr<base::SingleThreadTaskRunner>& glib_task_runner,
-      const scoped_refptr<base::SequencedTaskRunner>& io_task_runner,
+      const scoped_refptr<base::SequencedTaskRunner>& main_task_runner,
       const NetworkTrafficAnnotationTag& traffic_annotation) {
-    delegate_->SetUpAndFetchInitialConfig(glib_task_runner, io_task_runner,
+    delegate_->SetUpAndFetchInitialConfig(glib_task_runner, main_task_runner,
                                           traffic_annotation);
   }
   void OnCheckProxyConfigSettings() {

net/proxy_resolution/proxy_resolution_service.cc

@@ -1483,7 +1483,7 @@ void ProxyResolutionService::ForceReloadProxyConfig() {
 // static
 std::unique_ptr<ProxyConfigService>
 ProxyResolutionService::CreateSystemProxyConfigService(
-    const scoped_refptr<base::SequencedTaskRunner>& io_task_runner) {
+    const scoped_refptr<base::SequencedTaskRunner>& main_task_runner) {
 #if defined(OS_WIN)
   return std::make_unique<ProxyConfigServiceWin>(
       kSystemProxyConfigTrafficAnnotation);
@@ -1492,7 +1492,7 @@ ProxyResolutionService::CreateSystemProxyConfigService(
       kSystemProxyConfigTrafficAnnotation);
 #elif defined(OS_MACOSX)
   return std::make_unique<ProxyConfigServiceMac>(
-      io_task_runner, kSystemProxyConfigTrafficAnnotation);
+      main_task_runner, kSystemProxyConfigTrafficAnnotation);
 #elif defined(OS_CHROMEOS)
   LOG(ERROR) << "ProxyConfigService for ChromeOS should be created in "
              << "profile_io_data.cc::CreateProxyConfigService and this should "
@@ -1513,13 +1513,13 @@ ProxyResolutionService::CreateSystemProxyConfigService(
   // either |glib_default_loop| or an internal sequenced task runner) to
   // keep us updated when the proxy config changes.
   linux_config_service->SetupAndFetchInitialConfig(
-      glib_thread_task_runner, io_task_runner,
+      glib_thread_task_runner, main_task_runner,
       kSystemProxyConfigTrafficAnnotation);
 
   return std::move(linux_config_service);
 #elif defined(OS_ANDROID)
   return std::make_unique<ProxyConfigServiceAndroid>(
-      io_task_runner, base::ThreadTaskRunnerHandle::Get());
+      main_task_runner, base::ThreadTaskRunnerHandle::Get());
 #else
   LOG(WARNING) << "Failed to choose a system proxy settings fetcher "
                   "for this platform.";

net/proxy_resolution/proxy_resolution_service.h

@@ -272,9 +272,14 @@ class NET_EXPORT ProxyResolutionService
       const NetworkTrafficAnnotationTag& traffic_annotation);
 
   // Creates a config service appropriate for this platform that fetches the
-  // system proxy settings.
+  // system proxy settings. |main_task_runner| is the thread where the consumer
+  // of the ProxyConfigService will live.
+  //
+  // TODO(mmenke): Should this be a member of ProxyConfigService?
+  // The ProxyResolutionService may not even be in the same process as the
+  // system ProxyConfigService.
   static std::unique_ptr<ProxyConfigService> CreateSystemProxyConfigService(
-      const scoped_refptr<base::SequencedTaskRunner>& io_task_runner);
+      const scoped_refptr<base::SequencedTaskRunner>& main_task_runner);
 
   // This method should only be used by unit tests.
   void set_stall_proxy_auto_config_delay(base::TimeDelta delay) {