Fix for keeping lists structure

java/org/chromium/distiller/webdocument/filters/NestedElementRetainer.java

Index: java/org/chromium/distiller/webdocument/filters/NestedElementRetainer.java
diff --git a/java/org/chromium/distiller/webdocument/filters/NestedElementRetainer.java b/java/org/chromium/distiller/webdocument/filters/NestedElementRetainer.java
new file mode 100644
index 0000000000000000000000000000000000000000..47b590fd39645f7c2c09f132cbd77149959d802b
--- /dev/null
+++ b/java/org/chromium/distiller/webdocument/filters/NestedElementRetainer.java
@@ -0,0 +1,49 @@
+package org.chromium.distiller.webdocument.filters;
+
+import org.chromium.distiller.webdocument.WebDocument;
+import org.chromium.distiller.webdocument.WebElement;
+import org.chromium.distiller.webdocument.WebTag;
+
+import java.util.Stack;
+
+/**
+ * This class is used to identify what WebTag should be
+ * marked as <i>isContent</i> based on its {@link WebElement}s inside.
+ * A {@link WebTag} is content when:
+ * <ul>
+ *    <li>Has any {@link WebElement} which is content.</li>
+ *    <li>Has at least one nested {@link WebTag} which is content.</li>
+ * </ul>
+ */
+public class NestedElementRetainer {
+    public static void process(WebDocument document) {
+        boolean isContent = false;
+        int stackMark = -1;
+        Stack<WebTag> stack = new Stack<>();
+
+        for (WebElement e : document.getElements()) {
+            if (!(e instanceof WebTag)) {
+                if (!isContent) {
+                    isContent = e.getIsContent();
+                }
+            } else {
+                WebTag webTag = (WebTag) e;
+                if (webTag.isStartTag()) {
+                    webTag.setIsContent(isContent);
+                    stack.push(webTag);
+                    isContent = false;
+                } else {
+                    WebTag startWebTag = stack.pop();
+                    isContent |= stackMark >= stack.size();
+                    if (isContent) {
+                        stackMark = stack.size() - 1;
+                    }
+                    boolean wasContent = startWebTag.getIsContent();
+                    startWebTag.setIsContent(isContent);
+                    webTag.setIsContent(isContent);
+                    isContent = wasContent;
+                }
+            }
+        }
+    }
+}