Modify PluginURLFetcher to avoid accessing members after calling PluginStream methods.
Calling PluginStream methods may cause the instance to be deleted, causing a UAF.
Modify the code to update members before calling PluginStream methods.

BUG=304787

Review URL: https://codereview.chromium.org/26526002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227661 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227661