Change file op |ssize_t|s to FileOperationResult

util/file/string_file.h

Index: util/file/string_file.h
diff --git a/util/file/string_file.h b/util/file/string_file.h
index c2e18ada2787cb8b132c38f3381c921b68b4b106..05f57072540edca167634f85088af2799066782c 100644
--- a/util/file/string_file.h
+++ b/util/file/string_file.h
@@ -21,6 +21,7 @@
 
 #include "base/basictypes.h"
 #include "base/numerics/safe_math.h"
+#include "util/file/file_io.h"
 #include "util/file/file_reader.h"
 #include "util/file/file_writer.h"
 
@@ -50,7 +51,7 @@ class StringFile : public FileReaderInterface, public FileWriterInterface {
   void Reset();
 
   // FileReaderInterface:
-  ssize_t Read(void* data, size_t size) override;
+  FileOperationResult Read(void* data, size_t size) override;
 
   // FileWriterInterface:
   bool Write(const void* data, size_t size) override;