Avoid floating point when calculating the actual column count.

Source/core/layout/MultiColumnFragmentainerGroup.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 
 #include "core/layout/MultiColumnFragmentainerGroup.h"
 
 #include "core/layout/LayoutMultiColumnSet.h"
 
@@ skipping 262 matching lines @@
     // and will confuse and cause problems in other parts of the code.
     if (!m_columnHeight)
         return 1;
 
     // Our flow thread portion determines our column count. We have as many columns as needed to fit
     // all the content.
     LayoutUnit flowThreadPortionHeight = logicalHeightInFlowThread();
     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;
 }
 
 LayoutUnit MultiColumnFragmentainerGroup::heightAdjustedForRowOffset(LayoutUnit height) const
 {
     // Adjust for the top offset within the content box of the multicol container (containing
     // block), unless we're in the first set. We know that the top offset for the first set will be
     // zero, but if the multicol container has non-zero top border or padding, the set's top offset
     // (initially being 0 and relative to the border box) will be negative until it has been laid
@@ skipping 292 matching lines @@
     append(MultiColumnFragmentainerGroup(m_columnSet));
     return last();
 }
 
 void MultiColumnFragmentainerGroupList::deleteExtraGroups()
 {
     shrink(1);
 }
 
 } // namespace blink