Switch to standard integer types in ui/compositor/.

BUG=138542
[email protected]

Review URL: https://codereview.chromium.org/1548043003

Cr-Commit-Position: refs/heads/master@{#366835}
diff --git a/ui/compositor/layer_animator.cc b/ui/compositor/layer_animator.cc
index 691e020..2e2d457 100644
--- a/ui/compositor/layer_animator.cc
+++ b/ui/compositor/layer_animator.cc
@@ -4,6 +4,8 @@
 
 #include "ui/compositor/layer_animator.h"
 
+#include <stddef.h>
+
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/trace_event/trace_event.h"