Make various gfx classes more amenable to use as compile-time constants.

ui/gfx/geometry/vector2d.h

 // Copyright (c) 2012 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.
 
 // Defines a simple integer vector class.  This class is used to indicate a
 // distance in two dimensions between two points. Subtracting two points should
 // produce a vector, and adding a vector to a point produces the point at the
 // vector's distance from the original point.
 
 #ifndef UI_GFX_GEOMETRY_VECTOR2D_H_
 #define UI_GFX_GEOMETRY_VECTOR2D_H_
 
 #include <stdint.h>
 
 #include <iosfwd>
 #include <string>
 
 #include "ui/gfx/geometry/vector2d_f.h"
 #include "ui/gfx/gfx_export.h"
 
 namespace gfx {
 
 class GFX_EXPORT Vector2d {
  public:
-  Vector2d() : x_(0), y_(0) {}
-  Vector2d(int x, int y) : x_(x), y_(y) {}
+  constexpr Vector2d() : x_(0), y_(0) {}
+  constexpr Vector2d(int x, int y) : x_(x), y_(y) {}
 
-  int x() const { return x_; }
+  constexpr int x() const { return x_; }
   void set_x(int x) { x_ = x; }
 
-  int y() const { return y_; }
+  constexpr int y() const { return y_; }
   void set_y(int y) { y_ = y; }
 
   // True if both components of the vector are 0.
   bool IsZero() const;
 
   // Add the components of the |other| vector to the current vector.
   void Add(const Vector2d& other);
   // Subtract the components of the |other| vector from the current vector.
   void Subtract(const Vector2d& other);
 
@@ skipping 49 matching lines @@
 }
 
 // This is declared here for use in gtest-based unit tests but is defined in
 // the gfx_test_support target. Depend on that to use this in your unit test.
 // This should not be used in production code - call ToString() instead.
 void PrintTo(const Vector2d& vector, ::std::ostream* os);
 
 }  // namespace gfx
 
 #endif // UI_GFX_GEOMETRY_VECTOR2D_H_