Use correct container width as base for percentage margins.

Source/core/rendering/RenderBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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
@@ skipping 2226 matching lines @@
             containerWidthInInlineDirection = perpendicularContainingBlockLogicalHeight();
         LayoutUnit preferredWidth = computeLogicalWidthUsing(MainOrPreferredSize, styleToUse->logicalWidth(), containerWidthInInlineDirection, cb);
         computedValues.m_extent = constrainLogicalWidthByMinMax(preferredWidth, containerWidthInInlineDirection, cb);
     }
 
     // Margin calculations.
     if (hasPerpendicularContainingBlock || isFloating() || isInline()) {
         computedValues.m_margins.m_start = minimumValueForLength(styleToUse->marginStart(), containerLogicalWidth);
         computedValues.m_margins.m_end = minimumValueForLength(styleToUse->marginEnd(), containerLogicalWidth);
     } else {
-        LayoutUnit containerLogicalWidthForAutoMargins = containerLogicalWidth;
-        if (avoidsFloats() && cb->containsFloats())
-            containerLogicalWidthForAutoMargins = containingBlockAvailableLineWidth();
         bool hasInvertedDirection = cb->style()->isLeftToRightDirection() != style()->isLeftToRightDirection();
-        computeInlineDirectionMargins(cb, containerLogicalWidthForAutoMargins, computedValues.m_extent,
+        computeInlineDirectionMargins(cb, containerLogicalWidth, computedValues.m_extent,
             hasInvertedDirection ? computedValues.m_margins.m_end : computedValues.m_margins.m_start,
             hasInvertedDirection ? computedValues.m_margins.m_start : computedValues.m_margins.m_end);
     }
 
     if (!hasPerpendicularContainingBlock && containerLogicalWidth && containerLogicalWidth != (computedValues.m_extent + computedValues.m_margins.m_start + computedValues.m_margins.m_end)
         && !isFloating() && !isInline() && !cb->isFlexibleBoxIncludingDeprecated() && !cb->isRenderGrid()) {
         LayoutUnit newMargin = containerLogicalWidth - computedValues.m_extent - cb->marginStartForChild(this);
         bool hasInvertedDirection = cb->style()->isLeftToRightDirection() != style()->isLeftToRightDirection();
         if (hasInvertedDirection)
             computedValues.m_margins.m_start = newMargin;
@@ skipping 176 matching lines @@
     if (containingBlock->isFlexibleBox()) {
         // We need to let flexbox handle the margin adjustment - otherwise, flexbox
         // will think we're wider than we actually are and calculate line sizes wrong.
         // See also http://dev.w3.org/csswg/css-flexbox/#auto-margins
         if (marginStartLength.isAuto())
             marginStartLength.setValue(0);
         if (marginEndLength.isAuto())
             marginEndLength.setValue(0);
     }
 
+    LayoutUnit availableWidth = containerWidth;
+    if (avoidsFloats() && containingBlock->containsFloats())
+        availableWidth = containingBlockAvailableLineWidth();
+
     // Case One: The object is being centered in the containing block's available logical width.
-    if ((marginStartLength.isAuto() && marginEndLength.isAuto() && childWidth < containerWidth)
+    if ((marginStartLength.isAuto() && marginEndLength.isAuto() && childWidth < availableWidth)
         || (!marginStartLength.isAuto() && !marginEndLength.isAuto() && containingBlock->style()->textAlign() == WEBKIT_CENTER)) {
         // Other browsers center the margin box for align=center elements so we match them here.
         LayoutUnit marginStartWidth = minimumValueForLength(marginStartLength, containerWidth);
         LayoutUnit marginEndWidth = minimumValueForLength(marginEndLength, containerWidth);
-        LayoutUnit centeredMarginBoxStart = max<LayoutUnit>(0, (containerWidth - childWidth - marginStartWidth - marginEndWidth) / 2);
+        LayoutUnit centeredMarginBoxStart = max<LayoutUnit>(0, (availableWidth - childWidth - marginStartWidth - marginEndWidth) / 2);
         marginStart = centeredMarginBoxStart + marginStartWidth;
-        marginEnd = containerWidth - childWidth - marginStart + marginEndWidth;
+        marginEnd = availableWidth - childWidth - marginStart + marginEndWidth;
         return;
     }
 
     // Case Two: The object is being pushed to the start of the containing block's available logical width.
-    if (marginEndLength.isAuto() && childWidth < containerWidth) {
+    if (marginEndLength.isAuto() && childWidth < availableWidth) {
         marginStart = valueForLength(marginStartLength, containerWidth);
-        marginEnd = containerWidth - childWidth - marginStart;
+        marginEnd = availableWidth - childWidth - marginStart;
         return;
     }
 
     // Case Three: The object is being pushed to the end of the containing block's available logical width.
     bool pushToEndFromTextAlign = !marginEndLength.isAuto() && ((!containingBlockStyle->isLeftToRightDirection() && containingBlockStyle->textAlign() == WEBKIT_LEFT)
         || (containingBlockStyle->isLeftToRightDirection() && containingBlockStyle->textAlign() == WEBKIT_RIGHT));
-    if ((marginStartLength.isAuto() && childWidth < containerWidth) || pushToEndFromTextAlign) {
+    if ((marginStartLength.isAuto() && childWidth < availableWidth) || pushToEndFromTextAlign) {
         marginEnd = valueForLength(marginEndLength, containerWidth);
-        marginStart = containerWidth - childWidth - marginEnd;
+        marginStart = availableWidth - childWidth - marginEnd;
         return;
     }
 
     // Case Four: Either no auto margins, or our width is >= the container width (css2.1, 10.3.3).  In that case
     // auto margins will just turn into 0.
     marginStart = minimumValueForLength(marginStartLength, containerWidth);
     marginEnd = minimumValueForLength(marginEndLength, containerWidth);
 }
 
 static bool shouldFlipBeforeAfterMargins(const RenderStyle* containingBlockStyle, const RenderStyle* childStyle)
@@ skipping 2209 matching lines @@
         return 0;
 
     if (!layoutState && !flowThreadContainingBlock())
         return 0;
 
     RenderBlock* containerBlock = containingBlock();
     return containerBlock->offsetFromLogicalTopOfFirstPage() + logicalTop();
 }
 
 } // namespace WebCore