Add missing #include - fixes build on vs2019

Change-Id: I68bdf5ad1028ac344bca91c055045e5bf81318a3
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/29580
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Reviewed-by: dan sinclair <dsinclair@chromium.org>

src/inspector.h

diff --git a/src/inspector.h b/src/inspector.h
index db42b41..6631765 100644
--- a/src/inspector.h
+++ b/src/inspector.h
@@ -17,6 +17,7 @@
 
 #include <memory>
 #include <string>
+#include <tuple>
 #include <vector>
 
 #include "src/ast/module.h"