Marquee width should not change a fixed width of its container.

Source/core/layout/LayoutBlock.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. 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
@@ skipping 20 matching lines @@
 #include "core/dom/StyleEngine.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/editing/Editor.h"
 #include "core/editing/FrameSelection.h"
 #include "core/editing/htmlediting.h"
 #include "core/events/OverflowEvent.h"
 #include "core/fetch/ResourceLoadPriorityOptimizer.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
+#include "core/html/HTMLMarqueeElement.h"
 #include "core/layout/HitTestLocation.h"
 #include "core/layout/HitTestResult.h"
 #include "core/layout/LayoutAnalyzer.h"
 #include "core/layout/LayoutDeprecatedFlexibleBox.h"
 #include "core/layout/LayoutFlexibleBox.h"
 #include "core/layout/LayoutFlowThread.h"
 #include "core/layout/LayoutGrid.h"
 #include "core/layout/LayoutInline.h"
 #include "core/layout/LayoutMultiColumnSpannerPlaceholder.h"
 #include "core/layout/LayoutObject.h"
@@ skipping 1949 matching lines @@
 {
     if (childrenInline()) {
         // FIXME: Remove this const_cast.
         toLayoutBlockFlow(const_cast<LayoutBlock*>(this))->computeInlinePreferredLogicalWidths(minLogicalWidth, maxLogicalWidth);
     } else {
         computeBlockPreferredLogicalWidths(minLogicalWidth, maxLogicalWidth);
     }
 
     maxLogicalWidth = std::max(minLogicalWidth, maxLogicalWidth);
 
+    if (isHTMLMarqueeElement(node()) && toHTMLMarqueeElement(node())->isHorizontal())
+        minLogicalWidth = LayoutUnit();
+
     if (isTableCell()) {
         Length tableCellWidth = toLayoutTableCell(this)->styleOrColLogicalWidth();
         if (tableCellWidth.isFixed() && tableCellWidth.value() > 0)
             maxLogicalWidth = std::max(minLogicalWidth, adjustContentBoxLogicalWidthForBoxSizing(tableCellWidth.value()));
     }
 
     int scrollbarWidth = intrinsicScrollbarLogicalWidth();
     maxLogicalWidth += scrollbarWidth;
     minLogicalWidth += scrollbarWidth;
 }
@@ skipping 897 matching lines @@
 void LayoutBlock::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const LayoutObject* obj) const
 {
     showLayoutObject();
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 
 #endif
 
 } // namespace blink