make pending pixels aware of screen size so that visible area is always filled

mobile/app/mobile.js

@@ -37,9 +37,9 @@
 #filter substitution
 
 // for browser.xml binding
-pref("toolkit.browser.cachePixelX", 800);
+pref("toolkit.browser.cachePixelX", 400);
-pref("toolkit.browser.cachePixelY", 2000);
+pref("toolkit.browser.cachePixelY", 1000);
-pref("toolkit.browser.recacheRatio", 50);
+pref("toolkit.browser.recacheRatio", 60);
 
 pref("toolkit.defaultChromeURI", "chrome://browser/content/browser.xul");
 pref("general.useragent.compatMode.firefox", true);

mobile/chrome/content/bindings/browser.xml

@@ -834,8 +834,8 @@
             this._pendingPixelsX += x;
             this._pendingPixelsY += y;
 
-            if (Math.abs(this._pendingPixelsX) >= this._pendingThresholdX ||
+            if (Math.abs(this._pendingPixelsX) > Math.max(0, this._pendingThresholdX - bcr.width / 2) ||
-                Math.abs(this._pendingPixelsY) >= this._pendingThresholdY)
+                Math.abs(this._pendingPixelsY) > Math.max(0, this._pendingThresholdY - bcr.height / 2))
               this._updateCacheViewport();
           ]]>
         </body>