Call BrowserProcess::GetApplicationLocale() on the right thread.

GetApplicationLocale() should only be called on the UI thread. In
r303655, GetApplicationLocale() calls in ResolveUILanguageList() got
moved off the UI thread but nobody noticed because
GetApplicationLocale() didn't have any DCHECKs. In the process of adding
the DCHECKs, this issue now becomes apparent.

Fix the issue by calling GetApplicationLocale() on the UI thread first,
before posting a task to ResolveLanguageListInThreadPool(). This also
replaces 4 GetApplicationLocale() calls with 1. Rearrange the logic
inside ResolveLanguageListInThreadPool() slightly as well.

Bug: 1033644
Change-Id: I3c350c34cf253052bad18b850381e2c92003b7f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2036373Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738055}

chrome/browser/ui/webui/chromeos/login/l10n_util.cc

@@ -345,6 +345,7 @@ std::string CalculateSelectedLanguage(const std::string& requested_locale,
 }
 
 void ResolveLanguageListInThreadPool(
+    const std::string& locale,
     std::unique_ptr<chromeos::locale_util::LanguageSwitchResult>
         language_switch_result,
     const scoped_refptr<base::TaskRunner> task_runner,
@@ -353,14 +354,7 @@ void ResolveLanguageListInThreadPool(
                                                 base::BlockingType::MAY_BLOCK);
 
   std::string selected_language;
-  if (!language_switch_result) {
-    if (!g_browser_process->GetApplicationLocale().empty()) {
-      selected_language = g_browser_process->GetApplicationLocale();
-    } else {
-      selected_language =
-          StartupCustomizationDocument::GetInstance()->initial_locale_default();
-    }
-  } else {
+  if (language_switch_result) {
     if (language_switch_result->success) {
       if (language_switch_result->requested_locale ==
           language_switch_result->loaded_locale) {
@@ -373,14 +367,17 @@ void ResolveLanguageListInThreadPool(
     } else {
       selected_language = language_switch_result->loaded_locale;
     }
+  } else {
+    selected_language = !locale.empty()
+                            ? locale
+                            : StartupCustomizationDocument::GetInstance()
+                                  ->initial_locale_default();
   }
   const std::string selected_code =
-      selected_language.empty() ? g_browser_process->GetApplicationLocale()
-                                : selected_language;
+      selected_language.empty() ? locale : selected_language;
 
   const std::string list_locale =
-      language_switch_result ? language_switch_result->loaded_locale
-                             : g_browser_process->GetApplicationLocale();
+      language_switch_result ? language_switch_result->loaded_locale : locale;
   std::unique_ptr<base::ListValue> language_list(
       chromeos::GetUILanguageList(nullptr, selected_code));
 
@@ -433,7 +430,8 @@ void ResolveUILanguageList(
   base::PostTask(
       FROM_HERE, {base::ThreadPool(), base::MayBlock()},
       base::BindOnce(&ResolveLanguageListInThreadPool,
-                     base::Passed(&language_switch_result),
+                     g_browser_process->GetApplicationLocale(),
+                     std::move(language_switch_result),
                      base::SequencedTaskRunnerHandle::Get(), callback));
 }