AU: Support redirects.

BUG=5692
TEST=unit tests, gmerged on device, making sure update engine still works

Change-Id: If593f6efbd39452aa98b453f4d5489ce7d7d7fb9

Review URL: http://codereview.chromium.org/3161041
diff --git a/libcurl_http_fetcher.h b/libcurl_http_fetcher.h
index a4ed52f..8908638 100644
--- a/libcurl_http_fetcher.h
+++ b/libcurl_http_fetcher.h
@@ -20,6 +20,8 @@
 
 class LibcurlHttpFetcher : public HttpFetcher {
  public:
+  static const int kMaxRedirects = 10;
+
   LibcurlHttpFetcher()
       : curl_multi_handle_(NULL),
         curl_handle_(NULL),