Provide gtest printers for ui/gfx geometry types

ui/gfx/geometry/vector3d_f.h

Index: ui/gfx/geometry/vector3d_f.h
diff --git a/ui/gfx/geometry/vector3d_f.h b/ui/gfx/geometry/vector3d_f.h
index 8f8b75d91e7c858377ec21121efbc6729020bc54..637b6d91807287dfbbfb242e8e03bf49d94ae0d4 100644
--- a/ui/gfx/geometry/vector3d_f.h
+++ b/ui/gfx/geometry/vector3d_f.h
@@ -10,6 +10,7 @@
 #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"
@@ -119,6 +120,11 @@ inline Vector3dF ScaleVector3d(const Vector3dF& v, float scale) {
   return ScaleVector3d(v, scale, scale, scale);
 }
 
+// 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_