AppendToFile implementation.

base/file_util.h

Index: base/file_util.h
diff --git a/base/file_util.h b/base/file_util.h
index b6e634d6e1871dbcaec28f6a6e9e6cb859d9fc26..1eac1caa9975e3f2247859a9dfce562e3a46de21 100644
--- a/base/file_util.h
+++ b/base/file_util.h
@@ -378,6 +378,10 @@ BASE_EXPORT int WriteFile(const FilePath& filename, const char* data, int size);
 // Append the data to |fd|. Does not close |fd| when done.
 BASE_EXPORT int WriteFileDescriptor(const int fd, const char* data, int size);
 #endif
+// Append the given buffer into the file. Returns the number of bytes written,
+// or -1 on error.
+BASE_EXPORT int AppendToFile(const FilePath& filename,
+                             const char* data, int size);
 
 // Gets the current working directory for the process.
 BASE_EXPORT bool GetCurrentDirectory(FilePath* path);