Fix bug in posting code where the callback was overwritten by two different types of XHR posts, causing havoc.
Fix bug in posting code where the callback was overwritten by two different types of XHR posts, causing havoc.

git-svn-id: abd770af2affaf62930f25b244f6edafe8ddae5b@288 164481a5-15cb-f69f-4b93-856c5b7754c5

bpsinc-native/src_third_party_webpagereplay,colin-scott/web-page-replay,snorp/web-page-replay,snorp/web-page-replay,chromium/web-page-replay,colin-scott/web-page-replay,chromium/web-page-replay,bpsinc-native/src_third_party_webpagereplay,bpsinc-native/src_third_party_webpagereplay,ting-yuan/web-page-replay,ting-yuan/web-page-replay,andrey-malets/web-page-replay,andrey-malets/web-page-replay