arc: Fix mouse scroll on notification

Forward ScrollEvent/MouseWheelEvent to the hosting widget so that
it is processed and reaches the containing ScrollView.

Also not forward touch events to ArcCustomNotificationView since
a View is not supposed to receive touch events. This gets rid of
the NOTREACHED() warning in chrome log.

BUG=b/31115616
BUG=642501

Review-Url: https://codereview.chromium.org/2291193003
Cr-Commit-Position: refs/heads/master@{#415708}

ui/arc/notification/arc_custom_notification_view.cc

@@ -40,8 +40,34 @@ class ArcCustomNotificationView::EventForwarder : public ui::EventHandler {
       return;
     }
 
+    if (event->IsScrollEvent()) {
+      ForwardScrollEvent(event->AsScrollEvent());
+    } else if (event->IsMouseWheelEvent()) {
+      ForwardMouseWheelEvent(event->AsMouseWheelEvent());
+    } else if (!event->IsTouchEvent()) {
+      // Forward the rest events to |owner_| except touches because View
+      // should no longer receive touch events. See View::OnTouchEvent.
       owner_->OnEvent(event);
     }
+  }
+
+  void ForwardScrollEvent(ui::ScrollEvent* event) {
+    views::Widget* widget = owner_->GetWidget();
+    if (!widget)
+      return;
+
+    event->target()->ConvertEventToTarget(widget->GetNativeWindow(), event);
+    widget->OnScrollEvent(event);
+  }
+
+  void ForwardMouseWheelEvent(ui::MouseWheelEvent* event) {
+    views::Widget* widget = owner_->GetWidget();
+    if (!widget)
+      return;
+
+    event->target()->ConvertEventToTarget(widget->GetNativeWindow(), event);
+    widget->OnMouseEvent(event);
+  }
 
   ArcCustomNotificationView* const owner_;