Bug 1607984 - P5. Add missing nsIIdentChannel interface. r=mattwoodrow

Regressiong from bug 1607987. This prevented from QueryInterface(Ci.nsIIdentChannel) in JS on the channel.

Differential Revision: https://phabricator.services.mozilla.com/D70002

--HG--
extra : moz-landing-system : lando

netwerk/ipc/DocumentChannel.cpp

@@ -48,6 +48,7 @@ NS_IMPL_RELEASE(DocumentChannel)
 NS_INTERFACE_MAP_BEGIN(DocumentChannel)
   NS_INTERFACE_MAP_ENTRY(nsIRequest)
   NS_INTERFACE_MAP_ENTRY(nsIChannel)
+  NS_INTERFACE_MAP_ENTRY(nsIIdentChannel)
   NS_INTERFACE_MAP_ENTRY(nsITraceableChannel)
   NS_INTERFACE_MAP_ENTRY_CONCRETE(DocumentChannel)
   NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIRequest)