Fix threading bugs in product label UI.

chrome/browser/ui/webui/help/help_handler.cc

Index: chrome/browser/ui/webui/help/help_handler.cc
diff --git a/chrome/browser/ui/webui/help/help_handler.cc b/chrome/browser/ui/webui/help/help_handler.cc
index b88247f3f3061447b0ef0f9e38ef3f2e5bed1c6b..b7e9d962891bb28d2d342b9d2e2c979c4ff829a9 100644
--- a/chrome/browser/ui/webui/help/help_handler.cc
+++ b/chrome/browser/ui/webui/help/help_handler.cc
@@ -49,6 +49,7 @@
 #include "base/i18n/time_formatting.h"
 #include "base/prefs/pref_service.h"
 #include "base/sys_info.h"
+#include "base/task_runner_util.h"
 #include "chrome/browser/chromeos/ownership/owner_settings_service_chromeos.h"
 #include "chrome/browser/chromeos/ownership/owner_settings_service_chromeos_factory.h"
 #include "chrome/browser/chromeos/policy/browser_policy_connector_chromeos.h"
@@ -126,6 +127,19 @@ bool CanChangeChannel(Profile* profile) {
   return false;
 }
 
+// Reads the file containing the FCC label text, if found. Must be called from
+// the blocking pool.
+std::string ReadFCCLabelText() {
+  const base::FilePath asset_dir(FILE_PATH_LITERAL(chrome::kChromeOSAssetPath));
+  const base::FilePath label_file_path =
+      asset_dir.AppendASCII(kFCCLabelTextPath);
+
+  std::string contents;
+  if (base::ReadFileToString(label_file_path, &contents))
+    return contents;
+  return std::string();
+}
+
 #endif  // defined(OS_CHROMEOS)
 
 }  // namespace
@@ -403,9 +417,12 @@ void HelpHandler::OnPageLoaded(const base::ListValue* args) {
   version_updater_->GetChannel(false,
       base::Bind(&HelpHandler::OnTargetChannel, weak_factory_.GetWeakPtr()));
 
-  BrowserThread::PostTask(
-      BrowserThread::FILE, FROM_HERE,
-      base::Bind(&HelpHandler::LoadFCCLabelText, weak_factory_.GetWeakPtr()));
+  base::PostTaskAndReplyWithResult(
+      content::BrowserThread::GetBlockingPool(),
+      FROM_HERE,
+      base::Bind(&ReadFCCLabelText),
+      base::Bind(&HelpHandler::OnFCCLabelTextRead,
+                 weak_factory_.GetWeakPtr()));
 #endif
 }
 
@@ -587,16 +604,13 @@ void HelpHandler::OnTargetChannel(const std::string& channel) {
       "help.HelpPage.updateTargetChannel", base::StringValue(channel));
 }
 
-void HelpHandler::LoadFCCLabelText() {
-  base::FilePath path(std::string(chrome::kChromeOSAssetPath) +
-                      kFCCLabelTextPath);
-  std::string contents;
-  if (base::ReadFileToString(path, &contents)) {
-    // Remove unnecessary whitespace.
-    base::StringValue label(base::CollapseWhitespaceASCII(contents, true));
-    web_ui()->CallJavascriptFunction("help.HelpPage.setProductLabelText",
-                                     label);
-  }
+void HelpHandler::OnFCCLabelTextRead(std::string text) {
+  // Remove unnecessary whitespace.
+  text = base::CollapseWhitespaceASCII(text, true);
+  if (text.empty())
+    return;
+  base::StringValue label(text);
+  web_ui()->CallJavascriptFunction("help.HelpPage.setProductLabelText", label);
 }
 
 #endif // defined(OS_CHROMEOS)