Fix threading issue with Font Service bindings

This ensures that content::ConnectToFontService() always posts binding
operations to the same SequencedTaskRunner rather than using an
arbitrary runner per call.

Bug: 995144
Change-Id: Ic6f3947f056f028cb2febec875dd26eb8b870e82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1761555Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#688640}

chrome/browser/site_isolation/site_per_process_interactive_browsertest.cc

@@ -266,14 +266,8 @@ IN_PROC_BROWSER_TEST_F(SitePerProcessInteractiveBrowserTest,
 //
 // The test then presses <tab> six times to cycle through focused elements 1-6.
 // The test then repeats this with <shift-tab> to cycle in reverse order.
-#if defined(THREAD_SANITIZER)
-// TODO(crbug.com/995144): Fix the data race reported by TSan.
-#define MAYBE_SequentialFocusNavigation DISABLED_SequentialFocusNavigation
-#else
-#define MAYBE_SequentialFocusNavigation SequentialFocusNavigation
-#endif
 IN_PROC_BROWSER_TEST_F(SitePerProcessInteractiveBrowserTest,
-                       MAYBE_SequentialFocusNavigation) {
+                       SequentialFocusNavigation) {
   GURL main_url(embedded_test_server()->GetURL(
       "a.com", "/cross_site_iframe_factory.html?a(b,c)"));
   ui_test_utils::NavigateToURL(browser(), main_url);

content/browser/font_service.cc

@@ -12,6 +12,14 @@ namespace content {
 
 namespace {
 
+base::SequencedTaskRunner* GetServiceTaskRunner() {
+  static base::NoDestructor<scoped_refptr<base::SequencedTaskRunner>>
+      task_runner{base::CreateSequencedTaskRunner(
+          {base::ThreadPool(), base::MayBlock(), base::WithBaseSyncPrimitives(),
+           base::TaskPriority::USER_BLOCKING})};
+  return task_runner->get();
+}
+
 void BindToBackgroundFontService(
     mojo::PendingReceiver<font_service::mojom::FontService> receiver) {
   static base::NoDestructor<font_service::FontServiceApp> service;
@@ -22,11 +30,9 @@ void BindToBackgroundFontService(
 
 void ConnectToFontService(
     mojo::PendingReceiver<font_service::mojom::FontService> receiver) {
-  base::CreateSequencedTaskRunner({base::ThreadPool(), base::MayBlock(),
-                                   base::WithBaseSyncPrimitives(),
-                                   base::TaskPriority::USER_BLOCKING})
-      ->PostTask(FROM_HERE, base::BindOnce(&BindToBackgroundFontService,
-                                           std::move(receiver)));
+  GetServiceTaskRunner()->PostTask(
+      FROM_HERE,
+      base::BindOnce(&BindToBackgroundFontService, std::move(receiver)));
 }
 
 }  // namespace content