Add missing header causing build error with GCC13

Bug: chromium:957519
Change-Id: I0146fdb18764b683b502e9804bce1c7b2ab05294
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/296980
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Auto-Submit: Bruno Pitrus <brunopitrus@hotmail.com>
Cr-Commit-Position: refs/heads/main@{#39536}
diff --git a/rtc_base/third_party/base64/base64.h b/rtc_base/third_party/base64/base64.h
index 4190a79..5d42513 100644
--- a/rtc_base/third_party/base64/base64.h
+++ b/rtc_base/third_party/base64/base64.h
@@ -12,6 +12,8 @@
 #ifndef RTC_BASE_THIRD_PARTY_BASE64_BASE64_H_
 #define RTC_BASE_THIRD_PARTY_BASE64_BASE64_H_
 
+#include <cstddef>
+#include <cstdint>
 #include <string>
 #include <vector>