Refactor button a bit to support different sizes. Use it for the overlaybox.

shell/view/frame/overlaybox.py

@@ -1,7 +1,6 @@
 import hippo
 
-from sugar.graphics import style
-from sugar.graphics.canvasicon import CanvasIcon
+from sugar.graphics.button import Button
 
 class OverlayBox(hippo.CanvasBox):
     def __init__(self, shell):
@@ -9,8 +8,7 @@ class OverlayBox(hippo.CanvasBox):
 
         self._shell = shell
 
-        icon = CanvasIcon(icon_name='theme:stock-chat')
-        style.apply_stylesheet(icon, 'frame.OverlayIcon')
+        icon = Button(icon_name='theme:stock-chat')
         icon.connect('activated', self._overlay_clicked_cb)
         self.append(icon)
 

shell/view/stylesheet.py

@@ -29,12 +29,6 @@ frame_ActivityIcon = {
     'scale'      : style.standard_icon_scale
 }
 
-frame_OverlayIcon = {
-    'box-width'  : grid.dimension(1),
-    'box-height' : grid.dimension(1),
-    'scale'      : style.standard_icon_scale
-}
-
 frame_ZoomIcon = {
     'box-width'  : grid.dimension(1),
     'box-height' : grid.dimension(1),