Prepare for late binding of SpdyHttpStreams.
* Move HostPortProxyPair to net/proxy/proxy_server.h.
* Have the Job assign the spdy_session_key to the Request when it's determined.
* Have the Job notify the HttpStreamFactoryImpl when a SpdySession becomes available.
Next steps:
* When HttpStreamFactoryImpl sees a SpdySession becomes available, service all applicable requests by examining their spdy_session_key.
* Introduce a new NetLog::Source for the late bound jobs.
* Have HttpStreamFactoryImpl create two Jobs instead of just 1 per Request if Alternate-Protocol is available.
BUG=54371,42669
TEST=existing
Review URL: http://codereview.chromium.org/
6577035
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@76107 0039d316-1c4b-4281-b951-d872f2087c98