Switch to standard integer types in chrome/browser/chromeos/.

BUG=138542
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Review URL: https://codereview.chromium.org/1547093002

Cr-Commit-Position: refs/heads/master@{#366838}
diff --git a/chrome/browser/chromeos/external_metrics.cc b/chrome/browser/chromeos/external_metrics.cc
index e36f17a..1a60716 100644
--- a/chrome/browser/chromeos/external_metrics.cc
+++ b/chrome/browser/chromeos/external_metrics.cc
@@ -4,6 +4,8 @@
 
 #include "chrome/browser/chromeos/external_metrics.h"
 
+#include <stddef.h>
+
 #include <map>
 #include <string>