Adds missing header to fix compilation error when compiling with use_custom_libcxx set to false.

Fixed: webrtc:12584
Change-Id: I8830095f887e7ee8887bc37106da847b60c1e996
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/211762
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33557}
diff --git a/modules/video_coding/decoding_state.h b/modules/video_coding/decoding_state.h
index b87fb2d..ec97294 100644
--- a/modules/video_coding/decoding_state.h
+++ b/modules/video_coding/decoding_state.h
@@ -11,6 +11,7 @@
 #ifndef MODULES_VIDEO_CODING_DECODING_STATE_H_
 #define MODULES_VIDEO_CODING_DECODING_STATE_H_
 
+#include <cstdint>
 #include <map>
 #include <set>
 #include <vector>