Fix preparing log file name.

src/base/platform/platform-win32.cc

Index: src/base/platform/platform-win32.cc
diff --git a/src/base/platform/platform-win32.cc b/src/base/platform/platform-win32.cc
index 5a6f2f1cbfcfab31ecc8b9d7768b9348fae6e806..07c0bc3ebf76423d2df3312fcfdd5617e3476f9e 100644
--- a/src/base/platform/platform-win32.cc
+++ b/src/base/platform/platform-win32.cc
@@ -575,6 +575,11 @@ bool OS::Remove(const char* path) {
 }
 
 
+bool OS::isDirectorySeparator(const char ch) {
+  return ch == '/' || ch == '\\';
+}
+
+
 FILE* OS::OpenTemporaryFile() {
   // tmpfile_s tries to use the root dir, don't use it.
   char tempPathBuffer[MAX_PATH];