reducers: Store interaction tokens

Consider the user repeatedly dwelling on and abandoning a link. Testing
whether or not the element has changed before modifying state is not
sufficient. Fortunately, we already generate a unique token and include
it in the LINK_DWELL action for use in the eventLogging reducer - the
so-called "interaction token".

Change-Id: Iae9544055f7eccb4f7f071797eb360bc3456861a

resources/ext.popups/reducers/preview.js

@@ -14,6 +14,7 @@
 				enabled: undefined,
 				activeLink: undefined,
 				activeEvent: undefined,
+				activeToken: '',
 				shouldShow: false,
 				isUserDwelling: false
 			};
@@ -32,6 +33,7 @@
 				return nextState( state, {
 					activeLink: action.el,
 					activeEvent: action.event,
+					activeToken: action.token,
 
 					// When the user dwells on a link with their keyboard, a preview is
 					// renderered, and then dwells on another link, the LINK_ABANDON_END

tests/qunit/ext.popups/reducers/preview.test.js

@@ -17,6 +17,7 @@
 				enabled: undefined,
 				activeLink: undefined,
 				activeEvent: undefined,
+				activeToken: '',
 				shouldShow: false,
 				isUserDwelling: false
 			}
@@ -61,7 +62,8 @@
 		var action = {
 			type: 'LINK_DWELL',
 			el: this.el,
-			event: {}
+			event: {},
+			token: '1234567890'
 		};
 
 		assert.deepEqual(
@@ -69,6 +71,7 @@
 			{
 				activeLink: action.el,
 				activeEvent: action.event,
+				activeToken: action.token,
 				shouldShow: false
 			},
 			'It should set active link and event as well as interaction info and hide the preview.'