Code review fixes for 599512 - Partial black thumbnails

--HG--
extra : rebase_source : b10e73ab21a4a1f37009ceeff360d3d644343de5

mobile/chrome/content/browser.js

@@ -2508,7 +2508,7 @@ Tab.prototype = {
 
     // Do not repaint thumbnail if we already painted for this load. Bad things
     // happen when we do async canvas draws in quick succession.
-    if (!browser || this._lastThumbnailWindow == browser.contentWindowId)
+    if (!browser || this._thumbnailWindowId == browser.contentWindowId)
       return;
 
     // Do not try to paint thumbnails if contentWindowWidth/Height have not been
@@ -2516,7 +2516,7 @@ Tab.prototype = {
     if (!browser.contentWindowWidth || !browser.contentWindowHeight)
       return;
 
-    this._lastThumbnailWindow = browser.contentWindowId;
+    this._thumbnailWindowId = browser.contentWindowId;
     this._chromeTab.updateThumbnail(browser, browser.contentWindowWidth, browser.contentWindowHeight);
   },
 

mobile/chrome/content/tabs.xml

@@ -53,9 +53,9 @@
             let canvas = document.getAnonymousElementByAttribute(this, "anonid", "canvas");
             let renderer = rendererFactory(browser, canvas)
             renderer.drawContent(function(ctx, callback) {
+              ctx.save();
               ctx.fillStyle = "white";
               ctx.fillRect(0, 0, tabWidth, tabHeight);
-              ctx.save();
               ctx.scale(tabWidth / width, tabHeight / height);
               callback(browser, 0, 0, width, height, "white");
               ctx.restore();