Fix logging of string16s from gfx namespace on Windows.

ui/gfx/selection_model.h

Index: ui/gfx/selection_model.h
===================================================================
--- ui/gfx/selection_model.h	(revision 137657)
+++ ui/gfx/selection_model.h	(working copy)
@@ -6,7 +6,7 @@
 #define UI_GFX_SELECTION_MODEL_H_
 #pragma once
 
-#include <iosfwd>
+#include <string>
 
 #include "ui/base/range/range.h"
 #include "ui/base/ui_export.h"
@@ -77,6 +77,8 @@
   bool operator==(const SelectionModel& sel) const;
   bool operator!=(const SelectionModel& sel) { return !(*this == sel); }
 
+  std::string ToString() const;
+
  private:
   friend class RenderText;
 
@@ -107,9 +109,6 @@
   LogicalCursorDirection caret_affinity_;
 };
 
-UI_EXPORT std::ostream& operator<<(std::ostream& out,
-                                   const SelectionModel& sel);
-
 }  // namespace gfx
 
 #endif  // UI_GFX_SELECTION_MODEL_H_