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 334 matching lines @@
     // width blocks within a cluster, since the narrower blocks would end up
     // larger than would otherwise be necessary).
     return renderer->isRenderView()
         || renderer->isFloating()
         || renderer->isOutOfFlowPositioned()
         || renderer->isTableCell()
         || renderer->isTableCaption()
         || renderer->isFlexibleBoxIncludingDeprecated()
         || renderer->hasColumns()
         || renderer->containingBlock()->isHorizontalWritingMode() != renderer->isHorizontalWritingMode()
-        || renderer->style()->isDisplayReplacedType();
+        || renderer->style()->isDisplayReplacedType()
+        || renderer->isTextArea();
     // FIXME: Tables need special handling to multiply all their columns by
     // the same amount even if they're different widths; so do hasColumns()
     // containers, and probably flexboxes...
 }
 
 bool TextAutosizer::isAutosizingCluster(const RenderBlock* renderer, TextAutosizingClusterInfo& parentClusterInfo)
 {
     ASSERT(isAutosizingContainer(renderer));
 
     return isNarrowDescendant(renderer, parentClusterInfo)
@@ skipping 103 matching lines @@
     // Don't autosize clusters that contain less than 4 lines of text (in
     // practice less lines are required, since measureDescendantTextWidth
     // assumes that characters are 1em wide, but most characters are narrower
     // than that, so we're overestimating their contribution to the linecount).
     //
     // This is to reduce the likelihood of autosizing things like headers and
     // footers, which can be quite visually distracting. The rationale is that
     // if a cluster contains very few lines of text then it's ok to have to zoom
     // in and pan from side to side to read each line, since if there are very
     // few lines of text you'll only need to pan across once or twice.
+    //
+    // An exception to the 4 lines of text are the textarea clusters, which are
+    // always autosized by default (i.e. threated as if they contain more than 4
+    // lines of text). This is to ensure that the text does not suddenly get
+    // autosized when the user enters more than 4 lines of text.
     float totalTextWidth = 0;
     const float minLinesOfText = 4;
     float minTextWidth = blockWidth * minLinesOfText;
     for (size_t i = 0; i < clusterInfos.size(); ++i) {
+        if (clusterInfos[i].root->isTextArea())
+            return true;
         measureDescendantTextWidth(clusterInfos[i].blockContainingAllText, clusterInfos[i], minTextWidth, totalTextWidth);
         if (totalTextWidth >= minTextWidth)
             return true;
     }
     return false;
 }
 
 void TextAutosizer::measureDescendantTextWidth(const RenderBlock* container, TextAutosizingClusterInfo& clusterInfo, float minTextWidth, float& textWidth)
 {
     bool skipLocalText = !containerShouldBeAutosized(container);
@@ skipping 113 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