An indicator in the address bar for SPDY usage by each website.
Shows a lightning icon in the address bar that's green if the page is SPDY enabled, and optionally gray if SPDY is disabled.
Currently it leverages the browser API for determining this, which relies on the protocol used for the initial page request.
**NEW in 0.6.0: added HTTP/2 icon [MATSUU Takuto]"
**NEW in 0.5.0: added SPDY3.1 icon [MATSUU Takuto]"
**NEW in 0.4.0: fix SPDY2 icon and added QUIC! [MATSUU Takuto]"
**NEW in 0.3.0: version numbers for SPDY 2 and 3 in the icon [MATSUU Takuto]**
**NEW in 0.2.0: option to disable gray icon when SPDY is not enabled**