Bug 1539311 - Fix incorrect parameter in the Windows Taskbar Previews code. r=Standard8

Differential Revision: https://phabricator.services.mozilla.com/D25013

--HG--
extra : moz-landing-system : lando

browser/modules/WindowsPreviewPerTab.jsm

@@ -148,7 +148,7 @@ function PreviewController(win, tab) {
   this.tab.addEventListener("TabAttrModified", this);
 
   XPCOMUtils.defineLazyGetter(this, "canvasPreview", function() {
-    let canvas = PageThumbs.createCanvas(this.win);
+    let canvas = PageThumbs.createCanvas(this.win.win);
     canvas.mozOpaque = true;
     return canvas;
   });
@@ -270,7 +270,7 @@ PreviewController.prototype = {
       let winWidth = this.win.width;
       let winHeight = this.win.height;
 
-      let composite = PageThumbs.createCanvas(this.win);
+      let composite = PageThumbs.createCanvas(this.win.win);
 
       // Use transparency, Aero glass is drawn black without it.
       composite.mozOpaque = false;

toolkit/components/thumbnails/PageThumbs.jsm

@@ -261,7 +261,7 @@ var PageThumbs = {
       return;
     }
     // The content is a local page, grab a thumbnail sync.
-    PageThumbUtils.createSnapshotThumbnail(aBrowser.ownerGlobal,
+    PageThumbUtils.createSnapshotThumbnail(aBrowser.contentWindow,
                                            aCanvas,
                                            aArgs);