Assert that CFX_ strings are pointer-size.

core/fxcrt/fx_basic_wstring.cpp

Index: core/fxcrt/fx_basic_wstring.cpp
diff --git a/core/fxcrt/fx_basic_wstring.cpp b/core/fxcrt/fx_basic_wstring.cpp
index 069b9fa42d43ac1c5b506682ddc439ab406e76cf..f3b430c7bff3d2d7fc78babc66e2f7e55e20adab 100644
--- a/core/fxcrt/fx_basic_wstring.cpp
+++ b/core/fxcrt/fx_basic_wstring.cpp
@@ -59,6 +59,9 @@ const FX_WCHAR* FX_wcsstr(const FX_WCHAR* haystack,
 
 }  // namespace
 
+static_assert(sizeof(CFX_WideString) <= sizeof(FX_WCHAR*),
+              "Strings must not require more space than pointers");
+
 CFX_WideString::CFX_WideString(const FX_WCHAR* pStr, FX_STRSIZE nLen) {
   if (nLen < 0)
     nLen = pStr ? FXSYS_wcslen(pStr) : 0;