Avoid floating point when calculating the actual column count.

Source/core/layout/MultiColumnFragmentainerGroup.cpp

Index: Source/core/layout/MultiColumnFragmentainerGroup.cpp
diff --git a/Source/core/layout/MultiColumnFragmentainerGroup.cpp b/Source/core/layout/MultiColumnFragmentainerGroup.cpp
index f72aed8e9ff4c97c425ad51281d6576fad697006..a290c6c7fec521a2aec6f4b541739fb7d53e37d4 100644
--- a/Source/core/layout/MultiColumnFragmentainerGroup.cpp
+++ b/Source/core/layout/MultiColumnFragmentainerGroup.cpp
@@ -280,7 +280,10 @@ unsigned MultiColumnFragmentainerGroup::actualColumnCount() const
     if (!flowThreadPortionHeight)
         return 1;
 
-    unsigned count = ceil(flowThreadPortionHeight.toFloat() / m_columnHeight.toFloat());
+    unsigned count = (flowThreadPortionHeight / m_columnHeight).floor();
+    // flowThreadPortionHeight may be saturated, so detect the remainder manually.
+    if (count * m_columnHeight < flowThreadPortionHeight)

[mstensho (USE GERRIT), 2015/08/17 11:18:00]

If you can suggest something that looks less silly, I'm all ears. :)

Could have used intMod(m_columnHeight, flowThreadPortionHeight), although that's
more expensive.

Not that this is a hot code path or anything, though.

Cannot use ceil() instead of floor() on the expression above, because the
fractional part may be so small it's not possible for LayoutUnit to hold it.
E.g. 1001px / 1000px = 1 (but we DO need 2 columns in that case).

[eae, 2015/08/17 21:34:53]

We could check if the value is LayoutUnit::max but that way we cannot
distinguish saturated from max. Perhaps we should reserve a value to indicate
saturation.

That's a question for another day though, for now I think this is probably the
best we can do.

+        count++;
     ASSERT(count >= 1);
     return count;
 }