[SPDY] Log SPDY priority for SYN_STREAMs

Also use different logging functions for SYN_REPLY and HEADER
frames.

BUG=307757
R=rch@chromium.org

Review URL: https://codereview.chromium.org/27425002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229005 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229005