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

Source/core/rendering/TextAutosizer.cpp

Index: Source/core/rendering/TextAutosizer.cpp
diff --git a/Source/core/rendering/TextAutosizer.cpp b/Source/core/rendering/TextAutosizer.cpp
index 6fd64b6f333e69ad97f40c075fee6f03a8277bd6..287a82701bc675069b5d1c890af5ec469d32d58e 100644
--- a/Source/core/rendering/TextAutosizer.cpp
+++ b/Source/core/rendering/TextAutosizer.cpp
@@ -375,6 +375,9 @@ bool TextAutosizer::containerShouldBeAutosized(const RenderBlock* container)
     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())
@@ -438,6 +441,14 @@ bool TextAutosizer::containerIsRowOfLinks(const RenderObject* 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.