Add fflush after writing to log (Issue 868).

src/log-utils.h

Index: src/log-utils.h
diff --git a/src/log-utils.h b/src/log-utils.h
index 8889f1b77a30b17f9e7ae3802a2ffeeb350c71e9..a4dde213bf46305fc72046edad23b142c89b7f94 100644
--- a/src/log-utils.h
+++ b/src/log-utils.h
@@ -132,6 +132,7 @@ class Log : public AllStatic {
     size_t rv = fwrite(msg, 1, length, output_handle_);
     ASSERT(static_cast<size_t>(length) == rv);
     USE(rv);
+    fflush(output_handle_);
     return length;
   }