Generate param traits size methods for IPC files in chrome/ (and traits it depends on).

extensions/common/extension_message_generator.cc

Index: extensions/common/extension_message_generator.cc
diff --git a/extensions/common/extension_message_generator.cc b/extensions/common/extension_message_generator.cc
index b066c4f6cb8c9952481f95faf982f405e0a48d4a..0ed6784781be13df8b213bc68ec2258003d34d27 100644
--- a/extensions/common/extension_message_generator.cc
+++ b/extensions/common/extension_message_generator.cc
@@ -14,6 +14,12 @@
 #include "ipc/struct_destructor_macros.h"
 #include "extensions/common/extension_message_generator.h"
 
+// Generate param traits size methods.
+#include "ipc/param_traits_size_macros.h"
+namespace IPC {
+#include "extensions/common/extension_message_generator.h"
+}
+
 // Generate param traits write methods.
 #include "ipc/param_traits_write_macros.h"
 namespace IPC {