Fix textarea font autosizing oscillation when the number of lines exceeds 4. The proposed fix is no…

Source/core/rendering/TextAutosizer.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 357 matching lines @@
 }
 
 bool TextAutosizer::containerShouldBeAutosized(const RenderBlock* container)
 {
     if (containerContainsOneOfTags(container, formInputTags()))
         return false;
 
     if (containerIsRowOfLinks(container))
         return false;
 
+    if (containerIsTextArea(container))
+        return false;
+
     // Don't autosize block-level text that can't wrap (as it's likely to
     // expand sideways and break the page's layout).
     if (!container->style()->autoWrap())
         return false;
 
     return !contentHeightIsConstrained(container);
 }
 
 bool TextAutosizer::containerContainsOneOfTags(const RenderBlock* container, const Vector<QualifiedName>& tags)
 {
@@ skipping 43 matching lines @@
             linkCount++;
             // Skip traversing descendants of the link.
             renderer = renderer->nextInPreOrderAfterChildren(container);
         } else
             renderer = nextInPreOrderSkippingDescendantsOfContainers(renderer, container);
     }
 
     return (linkCount >= 3);
 }
 
+bool TextAutosizer::containerIsTextArea(const RenderBlock* container)
+{
+    // Don't autosize textareas to prevent annoying oscillation when the entered texts exceeds
+    // 4 lines and the text inside the area suddenly gets boosted.
+    const RenderObject* parentBlock = (container->parent()) ? container->parent() : container;
+    return parentBlock->isTextArea();
+}
+
 bool TextAutosizer::contentHeightIsConstrained(const RenderBlock* container)
 {
     // FIXME: Propagate constrainedness down the tree, to avoid inefficiently walking back up from each box.
     // FIXME: This code needs to take into account vertical writing modes.
     // FIXME: Consider additional heuristics, such as ignoring fixed heights if the content is already overflowing before autosizing kicks in.
     for (; container; container = container->containingBlock()) {
         RenderStyle* style = container->style();
         if (style->overflowY() >= OSCROLL)
             return false;
         if (style->height().isSpecified() || style->maxHeight().isSpecified()) {
@@ skipping 155 matching lines @@
         if (i + 1 < clusterInfos.size()) {
             float currentWidth = clusterInfos[i].root->contentLogicalWidth();
             float nextWidth = clusterInfos[i + 1].root->contentLogicalWidth();
             if (currentWidth - nextWidth > maxWidthDifferenceWithinGroup)
                 groups.grow(groups.size() + 1);
         }
     }
 }
 
 } // namespace WebCore