js: Explicitly dispose all cairo contexts

Due to limitations and bugs in SpiderMonkey's GC, wrapper objects
for cairo contexts and similar may not get cleaned up immediately
after repainting, leading to leaking memory. Explicitly disposing
of such objects after they're not needed can clean up large portions
of memory for cairo surfaces.

https://bugzilla.gnome.org/show_bug.cgi?id=685513

js/gdm/loginDialog.js

@@ -532,6 +532,7 @@ const SessionListItem = new Lang.Class({
                           color.alpha / 255);
         cr.arc(width / 2, height / 2, width / 3, 0, 2 * Math.PI);
         cr.fill();
+        cr.$dispose();
     },
 
     _onClicked: function() {

js/ui/boxpointer.js

@@ -388,6 +388,8 @@ const BoxPointer = new Lang.Class({
             cr.setLineWidth(borderWidth);
             cr.stroke();
         }
+
+        cr.$dispose();
     },
 
     setPosition: function(sourceActor, alignment) {

js/ui/dateMenu.js

@@ -32,6 +32,7 @@ function _onVertSepRepaint (area)
     cr.setDash([1, 3], 1); // Hard-code for now
     cr.setLineWidth(stippleWidth);
     cr.stroke();
+    cr.$dispose();
 };
 
 const DateMenuButton = new Lang.Class({

js/ui/panel.js

@@ -865,8 +865,8 @@ const PanelCorner = new Lang.Class({
         let backgroundColor = node.get_color('-panel-corner-background-color');
         let borderColor = node.get_color('-panel-corner-border-color');
 
-        let noOverlap = borderColor.alpha == 0;
-        let offsetY = noOverlap ? borderWidth : 0;
+        let overlap = borderColor.alpha != 0;
+        let offsetY = overlap ? 0 : borderWidth;
 
         let cr = this.actor.get_context();
         cr.setOperator(Cairo.Operator.SOURCE);
@@ -890,9 +890,7 @@ const PanelCorner = new Lang.Class({
         Clutter.cairo_set_source_color(cr, over);
         cr.fill();
 
-        if (noOverlap)
-            return;
-
+        if (overlap) {
             let offset = borderWidth;
             Clutter.cairo_set_source_color(cr, backgroundColor);
 
@@ -901,6 +899,9 @@ const PanelCorner = new Lang.Class({
             cr.appendPath(savedPath);
             cr.fill();
             cr.restore();
+        }
+
+        cr.$dispose();
     },
 
     _styleChanged: function() {

js/ui/popupMenu.js

@@ -207,6 +207,7 @@ const PopupBaseMenuItem = new Lang.Class({
             color.alpha / 255);
         cr.arc(width / 2, height / 2, width / 3, 0, 2 * Math.PI);
         cr.fill();
+        cr.$dispose();
     },
 
     // This returns column widths in logical order (i.e. from the dot
@@ -604,6 +605,7 @@ const PopupSliderMenuItem = new Lang.Class({
             color.alpha / 255);
         cr.arc(handleX, handleY, handleRadius, 0, 2 * Math.PI);
         cr.fill();
+        cr.$dispose();
     },
 
     _startDragging: function(actor, event) {

js/ui/separator.js

@@ -30,5 +30,6 @@ const HorizontalSeparator = new Lang.Class({
         cr.setSource(pattern);
         cr.rectangle(margin, gradientOffset, gradientWidth, gradientHeight);
         cr.fill();
+        cr.$dispose();
     }
 });

js/ui/switcherPopup.js

@@ -637,5 +637,6 @@ function drawArrow(area, side) {
 
     Clutter.cairo_set_source_color(cr, bodyColor);
     cr.fill();
+    cr.$dispose();
 }