Make isVisible() faster and more accurate

java/org/chromium/distiller/DomUtil.java

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.distiller;
 
 import com.google.gwt.core.client.JsArray;
 import com.google.gwt.core.client.JsArrayString;
 import com.google.gwt.dom.client.AnchorElement;
 import com.google.gwt.dom.client.Document;
@@ skipping 77 matching lines @@
     /**
       * @Return The CSS style of an element after applying the active stylesheets and resolving any
       * basic computation the style's value(s) may contain.
       * @param el - DOM element
     */
     public static native Style getComputedStyle(Element el) /*-{
       return getComputedStyle(el, null);
     }-*/;
 
     public static boolean isVisible(Element e) {
-        Style style = getComputedStyle(e);
-        double opacity = JavaScript.parseFloat(style.getOpacity());
-        return !(style.getDisplay().equals("none") ||
-                style.getVisibility().equals("hidden") ||
-                opacity == 0.0F);
+        // Detect whether any of the ancestors has "display: none".
+        // Using offsetParent alone wouldn't work because it's also null when position is fixed.
+        // Using offsetHeight/Width alone makes sense in production, but we have too many
+        // zero-sized elements in our tests.
+        return e.getOffsetParent() != null || e.getOffsetHeight() != 0 || e.getOffsetWidth() != 0;
     }
 
     /*
      * We want to use jsni for direct access to javascript's innerText.  This avoids GWT's
      * implementation of Element::getInnerText(), which is intentionally different to mimic an old
      * IE behaviour, which returns text within <script> tags.
      */
     public static native String getInnerText(Node node) /*-{
         return node.innerText;
     }-*/;
@@ skipping 281 matching lines @@
     }-*/;
 
     public static native Document createHTMLDocument(Document doc) /*-{
         return doc.implementation.createHTMLDocument();
     }-*/;
 
     public static native Element getFirstElementChild(Document document) /*-{
         return document.firstElementChild;
     }-*/;
 }