Unify geometry test printers in a test support target.

Source/platform/geometry/FloatBox.h

Index: Source/platform/geometry/FloatBox.h
diff --git a/Source/platform/geometry/FloatBox.h b/Source/platform/geometry/FloatBox.h
index a5edd6043108029353fba267cf95a4b621bb1bf7..c070337353120b1c1bcd216feebeb85f410205b8 100644
--- a/Source/platform/geometry/FloatBox.h
+++ b/Source/platform/geometry/FloatBox.h
@@ -33,6 +33,7 @@
 #include "platform/geometry/FloatPoint3D.h"
 #include <algorithm>
 #include <cmath>
+#include <iosfwd>
 
 namespace blink {
 
@@ -176,6 +177,10 @@ inline bool operator!=(const FloatBox& a, const FloatBox& b)
     return !(a == b);
 }
 
+// Redeclared here to avoid ODR issues.
+// See platform/testing/GeometryPrinters.h.
+void PrintTo(const FloatBox&, std::ostream*);
+
 } // namespace blink
 
 #endif