Base: WritePlatformFile now retries the operation if

base/platform_file.h

Index: base/platform_file.h
===================================================================
--- base/platform_file.h	(revision 97736)
+++ base/platform_file.h	(working copy)
@@ -123,7 +123,8 @@
 
 // Writes the given buffer into the file at the given offset, overwritting any
 // data that was previously there. Returns the number of bytes written, or -1
-// on error.
+// on error. Note that this function automatically retries writing if it is
+// expected for the underlying platform to write less data than |size|.
 BASE_EXPORT int WritePlatformFile(PlatformFile file, int64 offset,
                                   const char* data, int size);