Move RunAllPendingInMessageLoop from ui_test_utils.h to test_utils.h, so that it can be reused by c…

chrome/browser/extensions/api/downloads/downloads_api_unittest.cc

Index: chrome/browser/extensions/api/downloads/downloads_api_unittest.cc
===================================================================
--- chrome/browser/extensions/api/downloads/downloads_api_unittest.cc	(revision 149002)
+++ chrome/browser/extensions/api/downloads/downloads_api_unittest.cc	(working copy)
@@ -968,7 +968,7 @@
   // be able to query the file icon.
   download_item->Cancel(true);
   // Let cleanup complete on the FILE thread.
-  ui_test_utils::RunAllPendingInMessageLoop(BrowserThread::FILE);
+  content::RunAllPendingInMessageLoop(BrowserThread::FILE);
   args = base::StringPrintf("[%d, {\"size\": 32}]", download_item->GetId());
   EXPECT_TRUE(RunFunctionAndReturnString(new DownloadsGetFileIconFunction(),
                                          args, &result_string));