Add a hook immediately before a new session is created

The hook allows other specs to get access to the session and the
capabilities immediately before the new session response is sent to
the local end. This allows them to set up any state that is connected
to the session, and update the value of any capabilities they own in
the response.

Author: jgraham

index.html

@@ -1379,6 +1379,17 @@ <h3>Extensions</h3>
 matched, or a non-null JSON-serializable value if the capability is
 matched.
 
+<p>Other specifications may also define a <dfn>WebDriver new
+session algorithm</dfn>, which are called just after a new session is
+created, and before the <a>new session</a> response is sent to the
+<a>remote end</a>. These algorithms are called with <var>session</var>
+representing the WebDriver session that will be established,
+and <var>capabilites</var>, the capabilities object that will be
+returned to the <a>remote end</a>. It is permitted for such an
+algorithm to modify any entry in the capabilities object with a name
+that's an <a>additional WebDriver capability</a> defined by the same
+specification.
+
 <p><a>Remote ends</a> may also introduce
  <dfn data-lt="extension capability">extension capabilities</dfn>
  that are extra <a>capabilities</a>
@@ -2350,6 +2361,10 @@ <h3 id=new-session><dfn data-lt="new sessions|creating a new session">New Sessio
 
  <li><p>Set the <a>current session</a> to <var>session</var>.
 
+ <li><p>Run any <a>WebDriver new session algorithm</a>defined in
+ external specifications, with arguments <var>session</var>
+ and <var>capabilities</var>.
+
  <li><p>Append <var>session</var> to <a>active sessions</a>.
 
  <li><p>Let <var>body</var> be a JSON <a>Object</a> initialised with: