Fix for ASSERTION FAILURE contentSize >=0

Source/core/layout/LayoutFlexibleBox.cpp

Index: Source/core/layout/LayoutFlexibleBox.cpp
diff --git a/Source/core/layout/LayoutFlexibleBox.cpp b/Source/core/layout/LayoutFlexibleBox.cpp
index 5de6becb21b9f66ef63b7ed635c9bea88309a265..2007f88f10c2df5dd3bed0cfa4fe3c4998264e0f 100644
--- a/Source/core/layout/LayoutFlexibleBox.cpp
+++ b/Source/core/layout/LayoutFlexibleBox.cpp
@@ -117,7 +117,9 @@ void LayoutFlexibleBox::computeIntrinsicLogicalWidths(LayoutUnit& minLogicalWidt
                 // For multiline, the min preferred width is if you put a break between each item.
                 minLogicalWidth = std::max(minLogicalWidth, minPreferredLogicalWidth);
             } else {
-                minLogicalWidth += minPreferredLogicalWidth;
+                // We add minPreferredLogicalWidth only if is positive. Adding negative widths does not make sense.

[cbiesinger, 2015/05/27 16:50:19]

minPreferredLogicalWidth should not be negative. Why is it?

I feel like I saw another CL that tried to fix something like that... Ah: That
was https://codereview.chromium.org/343173003/, which is now committed. It seems
that a similar change needs to be applied to whichever LayoutObject returns a
negative number here.

+                if (minPreferredLogicalWidth >= 0)
+                    minLogicalWidth += minPreferredLogicalWidth;
             }
         } else {
             minLogicalWidth = std::max(minPreferredLogicalWidth, minLogicalWidth);