Bug 627068 - Don't set displayport for background tabs [r=stechz]

mobile/chrome/content/bindings/browser.xml

@@ -769,8 +769,11 @@
            * fast scrolling. This syncs that up with the current projection viewport.
            */
           _updateCacheViewport: function() {
-            let contentView = this._contentView;
             let self = this.self;
+            if (!self.active)
+               return;
+
+            let contentView = this._contentView;
             let viewportSize = this._getViewportSize();
             let cacheWidth = self._cacheRatioWidth * viewportSize.width;
             let cacheHeight = self._cacheRatioHeight * viewportSize.height;

mobile/chrome/content/browser.js

@@ -2460,6 +2460,9 @@ function Tab(aURI, aParams) {
   // aParams is an object that contains some properties for the initial tab
   // loading like flags, a referrerURI, a charset or even a postData.
   this.create(aURI, aParams || {});
+
+  // default tabs to inactive (i.e. no display port)
+  this.active = false;
 }
 
 Tab.prototype = {