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

ui/gfx/geometry/vector3d_f.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 float 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_VECTOR3D_F_H_
 #define UI_GFX_GEOMETRY_VECTOR3D_F_H_
 
 #include <iosfwd>
 #include <string>
 
 #include "ui/gfx/geometry/vector2d_f.h"
 #include "ui/gfx/gfx_export.h"
 
 namespace gfx {
 
 class GFX_EXPORT Vector3dF {
  public:
-  Vector3dF();
-  Vector3dF(float x, float y, float z);
+  constexpr Vector3dF() : x_(0), y_(0), z_(0) {}
+  constexpr Vector3dF(float x, float y, float z) : x_(x), y_(y), z_(z) {}
 
-  explicit Vector3dF(const Vector2dF& other);
+  constexpr explicit Vector3dF(const Vector2dF& other)
+      : x_(other.x()), y_(other.y()), z_(0) {}
 
-  float x() const { return x_; }
+  constexpr float x() const { return x_; }
   void set_x(float x) { x_ = x; }
 
-  float y() const { return y_; }
+  constexpr float y() const { return y_; }
   void set_y(float y) { y_ = y; }
 
-  float z() const { return z_; }
+  constexpr float z() const { return z_; }
   void set_z(float z) { z_ = z; }
 
   // True if all components of the vector are 0.
   bool IsZero() const;
 
   // Add the components of the |other| vector to the current vector.
   void Add(const Vector3dF& other);
   // Subtract the components of the |other| vector from the current vector.
   void Subtract(const Vector3dF& other);
 
@@ skipping 87 matching lines @@
     const gfx::Vector3dF& normal);
 
 // 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 Vector3dF& vector, ::std::ostream* os);
 
 }  // namespace gfx
 
 #endif // UI_GFX_GEOMETRY_VECTOR3D_F_H_