Add ostream helpers for FX String classes.

core/include/fxcrt/fx_string.h

Index: core/include/fxcrt/fx_string.h
diff --git a/core/include/fxcrt/fx_string.h b/core/include/fxcrt/fx_string.h
index 91032f9d9773b4e955d6dc6218454739f1aab69d..524d7efde5b6f08dcec5c56b002d08473a7f29f2 100644
--- a/core/include/fxcrt/fx_string.h
+++ b/core/include/fxcrt/fx_string.h
@@ -18,6 +18,7 @@ class CFX_WideStringL;
 class CFX_ByteStringC : public CFX_Object
 {
 public:
+    typedef FX_CHAR value_type;
 
     CFX_ByteStringC()
     {
@@ -160,6 +161,7 @@ struct CFX_StringData {
 class CFX_ByteString : public CFX_Object
 {
 public:
+    typedef FX_CHAR value_type;
 
     CFX_ByteString()
     {
@@ -473,6 +475,7 @@ typedef CFX_StringBufTemplate<256> CFX_StringBuf256;
 class CFX_WideStringC : public CFX_Object
 {
 public:
+    typedef FX_WCHAR value_type;
 
     CFX_WideStringC()
     {
@@ -618,6 +621,7 @@ struct CFX_StringDataW {
 class CFX_WideString : public CFX_Object
 {
 public:
+    typedef FX_WCHAR value_type;
 
     CFX_WideString()
     {