Treat <table> widths of 0 as auto.

third_party/WebKit/Source/core/layout/LayoutTable.cpp

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 253 matching lines @@
         setMarginStart(computedValues.m_margins.m_start);
         setMarginEnd(computedValues.m_margins.m_end);
     }
 
     LayoutBlock* cb = containingBlock();
 
     LayoutUnit availableLogicalWidth = containingBlockLogicalWidthForContent() + (isOutOfFlowPositioned() ? cb->paddingLogicalWidth() : LayoutUnit());
     bool hasPerpendicularContainingBlock = cb->style()->isHorizontalWritingMode() != style()->isHorizontalWritingMode();
     LayoutUnit containerWidthInInlineDirection = hasPerpendicularContainingBlock ? perpendicularContainingBlockLogicalHeight() : availableLogicalWidth;
 
+    ASSERT(!style()->logicalWidth().isNegative());
+    if (style()->logicalWidth().isSpecified() && style()->logicalWidth().isZero()) {
+        mutableStyle()->setLogicalWidth(Length());

[dgrogan, 2016/02/09 03:27:19]

I'm not sure how much of a no-no this is, to mutate the style during layout.
Perhaps I should instead modify whatever transforms a negative specified width
into auto to do the same for a zero specified width? Do you know where that is?
I've not been able to find it yet.

[mstensho (USE GERRIT), 2016/02/09 10:52:45]

I think this is bad. We should really leave computed style alone. Negative
width? Do we have those? The parser shouldn't have allowed that, since it would
be a spec violation.

Non-positive widths as in zero, sure - but negative widths???

[dgrogan, 2016/02/10 02:47:56]

No, we don't have negative widths, which is why I added the ASSERT. Some code
below checks for negative widths though...

+    }
     Length styleLogicalWidth = style()->logicalWidth();
-    if ((styleLogicalWidth.isSpecified() && styleLogicalWidth.isPositive()) || styleLogicalWidth.isIntrinsic()) {

[dgrogan, 2016/02/09 03:27:19]

With the above change this clause is always true.

+    if (styleLogicalWidth.isSpecified() || styleLogicalWidth.isIntrinsic()) {
         setLogicalWidth(convertStyleLogicalWidthToComputedWidth(styleLogicalWidth, containerWidthInInlineDirection));
     } else {
         // Subtract out any fixed margins from our available width for auto width tables.
         LayoutUnit marginStart = minimumValueForLength(style()->marginStart(), availableLogicalWidth);
         LayoutUnit marginEnd = minimumValueForLength(style()->marginEnd(), availableLogicalWidth);
         LayoutUnit marginTotal = marginStart + marginEnd;
 
         // Subtract out our margins to get the available content width.
         LayoutUnit availableContentLogicalWidth = (containerWidthInInlineDirection - marginTotal).clampNegativeToZero();
         if (shrinkToAvoidFloats() && cb->isLayoutBlockFlow() && toLayoutBlockFlow(cb)->containsFloats() && !hasPerpendicularContainingBlock)
             availableContentLogicalWidth = shrinkLogicalWidthToAvoidFloats(marginStart, marginEnd, toLayoutBlockFlow(cb));
 
         // Ensure we aren't bigger than our available width.
         setLogicalWidth(LayoutUnit(std::min(availableContentLogicalWidth, maxPreferredLogicalWidth()).floor()));
     }
 
     // Ensure we aren't bigger than our max-width style.
     Length styleMaxLogicalWidth = style()->logicalMaxWidth();
     if ((styleMaxLogicalWidth.isSpecified() && !styleMaxLogicalWidth.isNegative()) || styleMaxLogicalWidth.isIntrinsic()) {

[dgrogan, 2016/02/10 02:47:56]

Like here: !styleMaxLogicalWidth.isNegative().

[mstensho (USE GERRIT), 2016/02/10 10:04:09]

o_O

We should probably turn that into an ASSERT some day.

         LayoutUnit computedMaxLogicalWidth = convertStyleLogicalWidthToComputedWidth(styleMaxLogicalWidth, availableLogicalWidth);
         setLogicalWidth(LayoutUnit(std::min(logicalWidth(), computedMaxLogicalWidth).floor()));
     }
 
     // Ensure we aren't smaller than our min preferred width. This MUST be done after 'max-width' as
     // we ignore it if it means we wouldn't accommodate our content.
     setLogicalWidth(LayoutUnit(std::max(logicalWidth(), minPreferredLogicalWidth()).floor()));
 
     // Ensure we aren't smaller than our min-width style.
     Length styleMinLogicalWidth = style()->logicalMinWidth();
@@ skipping 1150 matching lines @@
 
 LayoutUnit LayoutTable::paddingRight() const
 {
     if (collapseBorders())
         return LayoutUnit();
 
     return LayoutBlock::paddingRight();
 }
 
 } // namespace blink