[gimp/gtk3-port] app: set GDK_SCROLL_MASK on widgets that need scroll events

[Michael Natterer <mitch src gnome org>]

commit 20622deda6786b4a9605b52a93bec5ebd58442e9
Author: Michael Natterer <mitch gimp org>
Date:   Thu May 10 23:43:36 2018 +0200

    app: set GDK_SCROLL_MASK on widgets that need scroll events

 app/display/gimpcanvas.h         |    1 +
 app/widgets/gimpgradienteditor.c |    4 +++-
 app/widgets/gimpnavigationview.c |    1 +
 3 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/app/display/gimpcanvas.h b/app/display/gimpcanvas.h
index bfd8492..a4f02e8 100644
--- a/app/display/gimpcanvas.h
+++ b/app/display/gimpcanvas.h
@@ -26,6 +26,7 @@
                                 GDK_POINTER_MOTION_MASK      | \
                                 GDK_BUTTON_PRESS_MASK        | \
                                 GDK_BUTTON_RELEASE_MASK      | \
+                                GDK_SCROLL_MASK              | \
                                 GDK_STRUCTURE_MASK           | \
                                 GDK_ENTER_NOTIFY_MASK        | \
                                 GDK_LEAVE_NOTIFY_MASK        | \
diff --git a/app/widgets/gimpgradienteditor.c b/app/widgets/gimpgradienteditor.c
index 2dc14bb..d85f6fd 100644
--- a/app/widgets/gimpgradienteditor.c
+++ b/app/widgets/gimpgradienteditor.c
@@ -91,7 +91,8 @@
                               GDK_POINTER_MOTION_MASK      | \
                               GDK_POINTER_MOTION_HINT_MASK | \
                               GDK_BUTTON_PRESS_MASK        | \
-                              GDK_BUTTON_RELEASE_MASK)
+                              GDK_BUTTON_RELEASE_MASK      | \
+                              GDK_SCROLL_MASK)
 
 #define GRAD_CONTROL_EVENT_MASK (GDK_EXPOSURE_MASK            | \
                                  GDK_LEAVE_NOTIFY_MASK        | \
@@ -99,6 +100,7 @@
                                  GDK_POINTER_MOTION_HINT_MASK | \
                                  GDK_BUTTON_PRESS_MASK        | \
                                  GDK_BUTTON_RELEASE_MASK      | \
+                                 GDK_SCROLL_MASK              | \
                                  GDK_BUTTON1_MOTION_MASK)
 
 
diff --git a/app/widgets/gimpnavigationview.c b/app/widgets/gimpnavigationview.c
index d11a741..5033250 100644
--- a/app/widgets/gimpnavigationview.c
+++ b/app/widgets/gimpnavigationview.c
@@ -166,6 +166,7 @@ gimp_navigation_view_init (GimpNavigationView *view)
 {
   gtk_widget_set_can_focus (GTK_WIDGET (view), TRUE);
   gtk_widget_add_events (GTK_WIDGET (view),
+                         GDK_SCROLL_MASK         |
                          GDK_POINTER_MOTION_MASK |
                          GDK_KEY_PRESS_MASK);