fbcode: String.h -> UTF8String.h includes

Summary: Include the new `UTF8String.h` header where needed.

Reviewed By: Orvid

Differential Revision: D7473655

fbshipit-source-id: 9d1b820123a786d8eb3d6405a4ff35331de41694

folly/String.h

@@ -33,11 +33,6 @@
 #include <folly/ScopeGuard.h>
 #include <folly/Traits.h>
 
-// Temporary compatilibility shim; UTF8StringPiece is no longer provided by
-// this file, but we'll allow includes of this file to continue to "provide"
-// its definition during a brief period while include-sites are updated.
-#include <folly/UTF8String.h>
-
 // Compatibility function, to make sure toStdString(s) can be called
 // to convert a std::string or fbstring variable s into type std::string
 // with very little overhead if s was already std::string

folly/experimental/JSONSchemaTester.cpp

@@ -16,6 +16,7 @@
 #include <folly/experimental/JSONSchema.h>
 #include <folly/json.h>
 #include <fstream>
+#include <sstream>
 #include <string>
 
 /**