Componentize component_updater: Replace content::BrowserThread usage with task runners

chrome/browser/component_updater/url_fetcher_downloader.h

Index: chrome/browser/component_updater/url_fetcher_downloader.h
diff --git a/chrome/browser/component_updater/url_fetcher_downloader.h b/chrome/browser/component_updater/url_fetcher_downloader.h
index 2132aa3566f9f8ae6b1f9f4a83e3985c0901954f..3168c1a24255c78c72a18ee3322cc450b0369b75 100644
--- a/chrome/browser/component_updater/url_fetcher_downloader.h
+++ b/chrome/browser/component_updater/url_fetcher_downloader.h
@@ -8,6 +8,7 @@
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/threading/thread_checker.h"
 #include "base/time/time.h"
 #include "chrome/browser/component_updater/crx_downloader.h"
 #include "net/url_request/url_fetcher_delegate.h"
@@ -47,6 +48,8 @@ class UrlFetcherDownloader : public CrxDownloader,
   int64 downloaded_bytes_;
   int64 total_bytes_;
 
+  base::ThreadChecker thread_checker_;
+
   DISALLOW_COPY_AND_ASSIGN(UrlFetcherDownloader);
 };