Merge to XFA: Backfill some FX String/StringC unit tests for == and !=.

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 c98a77cfe144dc903bfd258586f4afb3dc68ac04..b4d7249209c481f25fc749d95eb4749d8d01d51c 100644
--- a/core/include/fxcrt/fx_string.h
+++ b/core/include/fxcrt/fx_string.h
@@ -182,7 +182,10 @@ struct CFX_StringData {
     FX_STRSIZE	m_nAllocLength;
     FX_CHAR		m_String[1];
 };
-class CFX_ByteString 
+
+// A mutable string with shared buffers using copy-on-write semantics that
+// avoids the cost of std::string's iterator stability guarantees.
+class CFX_ByteString
 {
 public:
     typedef FX_CHAR value_type;
@@ -595,7 +598,10 @@ struct CFX_StringDataW {
     FX_STRSIZE	m_nAllocLength;
     FX_WCHAR	m_String[1];
 };
-class CFX_WideString 
+
+// A mutable string with shared buffers using copy-on-write semantics that
+// avoids the cost of std::string's iterator stability guarantees.
+class CFX_WideString
 {
 public:
     typedef FX_WCHAR value_type;