Make the LayoutRect->FloatRect constructor explicit.

Source/platform/geometry/FloatRect.h

 /*
  * Copyright (C) 2003, 2006, 2007 Apple Inc.  All rights reserved.
  * Copyright (C) 2005 Nokia.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 42 matching lines @@
         InsideOrOnStroke,
         InsideButNotOnStroke
     };
 
     FloatRect() { }
     FloatRect(const FloatPoint& location, const FloatSize& size)
         : m_location(location), m_size(size) { }
     FloatRect(float x, float y, float width, float height)
         : m_location(FloatPoint(x, y)), m_size(FloatSize(width, height)) { }
     FloatRect(const IntRect&);
-    FloatRect(const LayoutRect&);
+    explicit FloatRect(const LayoutRect&);
     FloatRect(const SkRect&);
 
     static FloatRect narrowPrecision(double x, double y, double width, double height);
 
     FloatPoint location() const { return m_location; }
     FloatSize size() const { return m_size; }
 
     void setLocation(const FloatPoint& location) { m_location = location; }
     void setSize(const FloatSize& size) { m_size = size; }
 
@@ skipping 172 matching lines @@
 // Map supplied rect from srcRect to an equivalent rect in destRect.
 PLATFORM_EXPORT FloatRect mapRect(const FloatRect&, const FloatRect& srcRect, const FloatRect& destRect);
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/GeometryPrinters.h.
 void PrintTo(const FloatRect&, std::ostream*);
 
 } // namespace blink
 
 #endif