Fix login visual hitch on chromebook

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

Index: chrome/browser/ui/webui/chromeos/login/user_image_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/user_image_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/user_image_screen_handler.cc
index ee791742768337f46b600b9ff9d7d43bf7838126..656062e664de743a652beb888a3711490da5e69e 100644
--- a/chrome/browser/ui/webui/chromeos/login/user_image_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/user_image_screen_handler.cc
@@ -18,12 +18,15 @@
 #include "chrome/browser/ui/webui/web_ui_util.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/url_constants.h"
+#include "content/public/browser/browser_thread.h"
 #include "googleurl/src/gurl.h"
 #include "grit/generated_resources.h"
 #include "net/base/data_url.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/views/widget/widget.h"
 
+using content::BrowserThread;
+
 namespace chromeos {
 
 UserImageScreenHandler::UserImageScreenHandler()
@@ -190,6 +193,7 @@ void UserImageScreenHandler::HandleGetImages(const base::ListValue* args) {
 }
 
 void UserImageScreenHandler::HandlePhotoTaken(const base::ListValue* args) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   std::string image_url;
   if (!args || args->GetSize() != 1 || !args->GetString(0, &image_url))
     NOTREACHED();
@@ -207,7 +211,9 @@ void UserImageScreenHandler::HandlePhotoTaken(const base::ListValue* args) {
     image_decoder_->set_delegate(NULL);
   image_decoder_ = new ImageDecoder(this, raw_data,
                                     ImageDecoder::DEFAULT_CODEC);
-  image_decoder_->Start();
+  scoped_refptr<base::MessageLoopProxy> task_runner =
+      BrowserThread::GetMessageLoopProxyForThread(BrowserThread::UI);
+  image_decoder_->Start(task_runner);
 }
 
 void UserImageScreenHandler::HandleCheckCameraPresence(