metrics: fix build on Windows

Change-Id: Ia9bff58e6d856cab8919ffde752195e2e03fc8c0
diff --git a/tools/gen_merged_sql_metrics.py b/tools/gen_merged_sql_metrics.py
index 319d0d3..e806be6 100755
--- a/tools/gen_merged_sql_metrics.py
+++ b/tools/gen_merged_sql_metrics.py
@@ -104,6 +104,9 @@
     for path in sql_outputs.keys():
       name = os.path.basename(path)
       variable = filename_to_variable(os.path.splitext(name)[0])
+
+      # This is for Windows which has \ as a path separator.
+      path = path.replace("\\", "\\\\")
       output.write('\n  {{"{}", {}}},\n'.format(path, variable))
     output.write("};\n")