gtk: smoother editor-canvas resize

- call `on-size' on setting the canvas size, like Win32 and Cocoa,
   which mainly shows/hides auto-shown scrollbars more on time
   (e.g., DrRacket doesn't start with horizontal scrollbars that
   immediately disappear)
 - switch mouse tracking to "hint" mode, instead of catching every
   single mouse position
 - when queueing `on-size' methos in response to client-size changes,
   cancel and queued but undelivered calls; in the case of editor
   canvases, this doesn't really have an effect, due to the other
   `on-size' call
 Closes PR 11369, hopefully

collects/mred/private/wx/cocoa/canvas.rkt

@@ -457,6 +457,7 @@
          (reset-auto-scroll 0 0))
        (on-size))
 
+     ;; this `on-size' method is for `editor-canvas%', only:
      (define/public (on-size) (void))
 
      (define/public (show-scrollbars h? v?)

collects/mred/private/wx/gtk/canvas.rkt

@@ -239,7 +239,7 @@
            [ignored-name #f]
            [gl-config #f])
 
-     (inherit get-gtk set-size get-size get-client-size 
+     (inherit get-gtk get-size get-client-size 
               get-top-win
               set-auto-size 
               adjust-client-delta infer-client-delta
@@ -336,6 +336,10 @@
                                         (list client-gtk))))])
 
      (set-size x y w h)
+
+     (define/override (set-size x y w h)
+       (super set-size x y w h)
+       (on-size))
      
      (define dc (new dc% [canvas this] [transparent? (memq 'transparent style)]))
 
@@ -361,7 +365,7 @@
                                                     GDK_KEY_RELEASE_MASK
                                                     GDK_BUTTON_PRESS_MASK
                                                     GDK_BUTTON_RELEASE_MASK
-                                                    GDK_POINTER_MOTION_MASK
+                                                    GDK_POINTER_MOTION_HINT_MASK
                                                     GDK_FOCUS_CHANGE_MASK
                                                     GDK_ENTER_NOTIFY_MASK
                                                     GDK_LEAVE_NOTIFY_MASK))
@@ -486,6 +490,7 @@
      (define/override (on-client-size w h) 
        (on-size))
 
+     ;; this `on-size' method is for `editor-canvas%', only:
      (define/public (on-size) (void))
 
      (define/public (show-scrollbars h? v?)

collects/mred/private/wx/gtk/client-window.rkt

@@ -36,13 +36,19 @@
 
     (define/public (on-client-size w h) (void))
 
+    (define client-size-key #f)
+
     (define/public (save-client-size x y w h)
       ;; Called in the Gtk event-loop thread
       (set! client-x x)
       (set! client-y y)
-      (queue-window-event this (lambda () 
+      (when client-size-key (set-box! client-size-key #f))
-				 (internal-on-client-size w h)
+      (let ([key (box #t)])
-				 (on-client-size w h))))
+        (set! client-size-key key)
+        (queue-window-event this (lambda () 
+                                   (when (unbox key)
+                                     (internal-on-client-size w h)
+                                     (on-client-size w h))))))
 
     (define/public (internal-on-client-size w h)
       (void))

collects/mred/private/wx/gtk/panel.rkt

@@ -82,7 +82,7 @@
     (connect-key-and-mouse gtk)
     (gtk_widget_add_events gtk (bitwise-ior GDK_BUTTON_PRESS_MASK
                                             GDK_BUTTON_RELEASE_MASK
-                                            GDK_POINTER_MOTION_MASK
+                                            GDK_POINTER_MOTION_HINT_MASK
                                             GDK_FOCUS_CHANGE_MASK
                                             GDK_ENTER_NOTIFY_MASK
                                             GDK_LEAVE_NOTIFY_MASK))

collects/mred/private/wx/win32/canvas.rkt

@@ -249,6 +249,7 @@
            (MoveWindow combo-hwnd 0 0 (max 1 w) (- h 2) #t)))
        (on-size))
 
+     ;; this `on-size' method is for `editor-canvas%', only:
      (define/public (on-size) (void))
 
      ;; The `queue-paint' and `paint-children' methods