Try to get LayoutUnit.h compiling on clang/win bots after VS2015 switch.

third_party/WebKit/Source/platform/LayoutUnit.h

 /*
  * Copyright (c) 2012, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 44 matching lines @@
 while (0)
 
 #endif
 
 static const int kLayoutUnitFractionalBits = 6;
 static const int kFixedPointDenominator = 1 << kLayoutUnitFractionalBits;
 
 const int intMaxForLayoutUnit = INT_MAX / kFixedPointDenominator;
 const int intMinForLayoutUnit = INT_MIN / kFixedPointDenominator;
 
+// TODO(thakis): Remove these two lines once http://llvm.org/PR26504 is resolved
+class LayoutUnit;
+inline bool operator<(const LayoutUnit&, const LayoutUnit&);
+
 class LayoutUnit {
     DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
 public:
     LayoutUnit() : m_value(0) { }
     // TODO(leviw): All of the below constructors should be explicit. crbug.com/581254
     LayoutUnit(int value) { setValue(value); }
     LayoutUnit(unsigned short value) { setValue(value); }
     LayoutUnit(unsigned value) { setValue(value); }
     LayoutUnit(unsigned long value) { m_value = clampTo<int>(value * kFixedPointDenominator); }
     LayoutUnit(unsigned long long value) { m_value = clampTo<int>(value * kFixedPointDenominator); }
@@ skipping 727 matching lines @@
     if (value >= max)
         return max;
     if (value <= min)
         return min;
     return value;
 }
 
 } // namespace blink
 
 #endif // LayoutUnit_h