Bring back overloading to print String8/16.

Change-Id: Iecab20db2b8574d5f1e6fdefdc2c8d4ce6c37121
diff --git a/include/hwbinder/TextOutput.h b/include/hwbinder/TextOutput.h
index de2fbbe..974a194 100644
--- a/include/hwbinder/TextOutput.h
+++ b/include/hwbinder/TextOutput.h
@@ -25,6 +25,9 @@
 // ---------------------------------------------------------------------------
 namespace android {
 
+class String8;
+class String16;
+
 class TextOutput
 {
 public:
@@ -76,6 +79,8 @@
 TextOutput& operator<<(TextOutput& to, double);
 TextOutput& operator<<(TextOutput& to, TextOutputManipFunc func);
 TextOutput& operator<<(TextOutput& to, const void*);
+TextOutput& operator<<(TextOutput& to, const String8& val);
+TextOutput& operator<<(TextOutput& to, const String16& val);
 
 class TypeCode 
 {