Make mouse wheel events trigger WebContentsObserver::DidGetUserInteraction.

content/public/browser/web_contents_observer.h

 // Copyright (c) 2012 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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_
 
 #include "base/process/kill.h"
 #include "base/process/process_handle.h"
 #include "content/common/content_export.h"
@@ skipping 301 matching lines @@
   // invokes this method. If there are ongoing navigations, their respective
   // failure methods will also be invoked.
   virtual void NavigationStopped() {}
 
   // This indicates that the next navigation was triggered by a user gesture.
   // TODO(dominickn): remove this method in favor of DidGetUserInteraction,
   // with the appropriate filtering by input event type.
   virtual void DidGetUserGesture() {}
 
   // Called when there has been direct user interaction with the WebContents.
-  // Direct user input includes 1) any mouse down event; 2) any raw key down
-  // event; and 3) any gesture tap event (including taps and scrolls).
+  // The type argument specifies the kind of interaction. Direct user input
+  // signalled through this callback includes:
+  // 1) any mouse down event (blink::WebInputEvent::MouseDown);
+  // 2) the start of a mouse wheel scroll (blink::WebInputEvent::MouseWheel);

[nasko, 2015/11/03 20:45:59]

It isn't really the start, is it? It is the first even in an interval. If I
scroll really slowly, such that each event is delivered right after the time
elapsed, wouldn't it result in another event fired?

[dominickn, 2015/11/03 21:29:42]

Yes. I've updated this comment to match.

+  // 3) any raw key down event (blink::WebInputEvent::RawKeyDown); and
+  // 4) any gesture tap event (blink::WebInputEvent::GestureTapDown).
   virtual void DidGetUserInteraction(const blink::WebInputEvent::Type type) {}
 
   // This method is invoked when a RenderViewHost of this WebContents was
   // configured to ignore UI events, and an UI event took place.
   virtual void DidGetIgnoredUIEvent() {}
 
   // These methods are invoked every time the WebContents changes visibility.
   virtual void WasShown() {}
   virtual void WasHidden() {}
 
@@ skipping 129 matching lines @@
   void ResetWebContents();
 
   WebContentsImpl* web_contents_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsObserver);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_