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

ui/gfx/geometry/box_f.h

Index: ui/gfx/geometry/box_f.h
diff --git a/ui/gfx/geometry/box_f.h b/ui/gfx/geometry/box_f.h
index deb359abdd30ad8d513148ea9e3d10babdde46e9..dff23c0f4f840bc7aed213d2936c83d0815fef6c 100644
--- a/ui/gfx/geometry/box_f.h
+++ b/ui/gfx/geometry/box_f.h
@@ -17,30 +17,33 @@ namespace gfx {
 // the camera.
 class GFX_EXPORT BoxF {
  public:
-  BoxF()
+  constexpr BoxF()
       : width_(0.f),
         height_(0.f),
         depth_(0.f) {}
 
-  BoxF(float width, float height, float depth)
+  constexpr BoxF(float width, float height, float depth)
       : width_(width < 0 ? 0 : width),
         height_(height < 0 ? 0 : height),
         depth_(depth < 0 ? 0 : depth) {}
 
-  BoxF(float x, float y, float z, float width, float height, float depth)
+  constexpr BoxF(float x,
+                 float y,
+                 float z,
+                 float width,
+                 float height,
+                 float depth)
       : origin_(x, y, z),
         width_(width < 0 ? 0 : width),
         height_(height < 0 ? 0 : height),
         depth_(depth < 0 ? 0 : depth) {}
 
-  BoxF(const Point3F& origin, float width, float height, float depth)
+  constexpr BoxF(const Point3F& origin, float width, float height, float depth)
       : origin_(origin),
         width_(width < 0 ? 0 : width),
         height_(height < 0 ? 0 : height),
         depth_(depth < 0 ? 0 : depth) {}
 
-  ~BoxF() {}
-
   // Scales all three axes by the given scale.
   void Scale(float scale) {
     Scale(scale, scale, scale);
@@ -66,27 +69,27 @@ class GFX_EXPORT BoxF {
 
   std::string ToString() const;
 
-  float x() const { return origin_.x(); }
+  constexpr float x() const { return origin_.x(); }

[danakj, 2016/06/10 00:36:47]

is this constexpr and const not redundant? Why is it not placed where "const" is
currently?

[vmpstr, 2016/06/10 00:46:15]

I think in C++14, non-static constexpr member function does not have to be
implicitly const, so maybe keep it as future proofing? 

[Peter Kasting, 2016/06/10 05:50:06]

No, they're not redundant.  Originally, constexpr implied const as you expect
(and as I expected originally).  This was removed in N3598.  More detail is
available at http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3598.html
.

MSVC 2015 will actually warn you that you've written a constexpr-but-not-const
function and ask if that's really what you intend.

   void set_x(float x) { origin_.set_x(x); }
 
-  float y() const { return origin_.y(); }
+  constexpr float y() const { return origin_.y(); }
   void set_y(float y) { origin_.set_y(y); }
 
-  float z() const { return origin_.z(); }
+  constexpr float z() const { return origin_.z(); }
   void set_z(float z) { origin_.set_z(z); }
 
-  float width() const { return width_; }
+  constexpr float width() const { return width_; }
   void set_width(float width) { width_ = width < 0 ? 0 : width; }
 
-  float height() const { return height_; }
+  constexpr float height() const { return height_; }
   void set_height(float height) { height_ = height < 0 ? 0 : height; }
 
-  float depth() const { return depth_; }
+  constexpr float depth() const { return depth_; }
   void set_depth(float depth) { depth_ = depth < 0 ? 0 : depth; }
 
-  float right() const { return x() + width(); }
-  float bottom() const { return y() + height(); }
-  float front() const { return z() + depth(); }
+  constexpr float right() const { return x() + width(); }
+  constexpr float bottom() const { return y() + height(); }
+  constexpr float front() const { return z() + depth(); }
 
   void set_size(float width, float height, float depth) {
     width_ = width < 0 ? 0 : width;
@@ -94,7 +97,7 @@ class GFX_EXPORT BoxF {
     depth_ = depth < 0 ? 0 : depth;
   }
 
-  const Point3F& origin() const { return origin_; }
+  constexpr const Point3F& origin() const { return origin_; }
   void set_origin(const Point3F& origin) { origin_ = origin; }
 
   // Expands |this| to contain the given point, if necessary. Please note, even