Make mouse wheel events trigger WebContentsObserver::DidGetUserInteraction.

chrome/browser/engagement/site_engagement_helper.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/engagement/site_engagement_helper.h"
 
 #include "base/time/time.h"
 #include "base/trace_event/trace_event.h"
 #include "chrome/browser/engagement/site_engagement_service.h"
 #include "chrome/browser/engagement/site_engagement_service_factory.h"
@@ skipping 67 matching lines @@
   switch (type) {
     case blink::WebInputEvent::RawKeyDown:
       helper_->RecordUserInput(SiteEngagementMetrics::ENGAGEMENT_KEYPRESS);
       break;
     case blink::WebInputEvent::MouseDown:
       helper_->RecordUserInput(SiteEngagementMetrics::ENGAGEMENT_MOUSE);
       break;
     case blink::WebInputEvent::GestureTapDown:
       helper_->RecordUserInput(SiteEngagementMetrics::ENGAGEMENT_TOUCH_GESTURE);
       break;
+    case blink::WebInputEvent::MouseWheel:
+      helper_->RecordUserInput(SiteEngagementMetrics::ENGAGEMENT_WHEEL);
+      break;
     default:
       NOTREACHED();
   }
   Pause();
 }
 
 SiteEngagementHelper::~SiteEngagementHelper() {
   content::WebContents* contents = web_contents();
   if (contents)
     input_tracker_.Stop();
@@ skipping 63 matching lines @@
 
 // static
 void SiteEngagementHelper::SetSecondsTrackingDelayAfterNavigation(int seconds) {
   g_seconds_tracking_delay_after_navigation = seconds;
 }
 
 // static
 void SiteEngagementHelper::SetSecondsTrackingDelayAfterShow(int seconds) {
   g_seconds_tracking_delay_after_show = seconds;
 }