linux_aura: run IconLoader::ReadIcon on the UI thread.

chrome/browser/icon_loader_android.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/logging.h"
 #include "chrome/browser/icon_loader.h"
 
 // static
 IconGroupID IconLoader::ReadGroupIDFromFilepath(
     const base::FilePath& filepath) {
   NOTIMPLEMENTED();
   return 0;
 }
 
 bool IconLoader::IsIconMutableFromFilepath(const base::FilePath&) {
   return false;
 }
 
+// static
+content::BrowserThread::ID IconLoader::ReadIconThreadID() {
+  NOTIMPLEMENTED();
+  return content::BrowserThread::FILE;
+}
+
 void IconLoader::ReadIcon() {
   NOTIMPLEMENTED();
 }