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

ui/gfx/geometry/quad_f.h

Index: ui/gfx/geometry/quad_f.h
diff --git a/ui/gfx/geometry/quad_f.h b/ui/gfx/geometry/quad_f.h
index f9eb3bc662b2c88f635f49f18af228e90886cf8b..18328c9c0c3858989473a7d68ebb640be67e4ef9 100644
--- a/ui/gfx/geometry/quad_f.h
+++ b/ui/gfx/geometry/quad_f.h
@@ -23,14 +23,14 @@ namespace gfx {
 // axis-aligned, unlike a Rect.
 class GFX_EXPORT QuadF {
  public:
-  QuadF() {}
-  QuadF(const PointF& p1, const PointF& p2, const PointF& p3, const PointF& p4)
-      : p1_(p1),
-        p2_(p2),
-        p3_(p3),
-        p4_(p4) {}
-
-  explicit QuadF(const RectF& rect)
+  constexpr QuadF() = default;
+  constexpr QuadF(const PointF& p1,
+                  const PointF& p2,
+                  const PointF& p3,
+                  const PointF& p4)
+      : p1_(p1), p2_(p2), p3_(p3), p4_(p4) {}
+
+  constexpr explicit QuadF(const RectF& rect)
       : p1_(rect.x(), rect.y()),
         p2_(rect.right(), rect.y()),
         p3_(rect.right(), rect.bottom()),
@@ -43,10 +43,10 @@ class GFX_EXPORT QuadF {
   void set_p3(const PointF& p) { p3_ = p; }
   void set_p4(const PointF& p) { p4_ = p; }
 
-  const PointF& p1() const { return p1_; }
-  const PointF& p2() const { return p2_; }
-  const PointF& p3() const { return p3_; }
-  const PointF& p4() const { return p4_; }
+  constexpr const PointF& p1() const { return p1_; }
+  constexpr const PointF& p2() const { return p2_; }
+  constexpr const PointF& p3() const { return p3_; }
+  constexpr const PointF& p4() const { return p4_; }
 
   // Returns true if the quad is an axis-aligned rectangle.
   bool IsRectilinear() const;