Mojo: add support for disallowing sync calls for a process.

mojo/public/cpp/bindings/lib/interface_endpoint_client.cc

Index: mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
diff --git a/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc b/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
index 90fc3f3ff7e24020b6beec6654cd3a669f7176f4..8dba64324413de2fe5aa22543690e0d35088fcd7 100644
--- a/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
+++ b/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
@@ -17,6 +17,7 @@
 #include "mojo/public/cpp/bindings/associated_group.h"
 #include "mojo/public/cpp/bindings/lib/interface_endpoint_controller.h"
 #include "mojo/public/cpp/bindings/lib/multiplex_router.h"
+#include "mojo/public/cpp/bindings/sync_call_restrictions.h"
 
 namespace mojo {
 namespace internal {
@@ -229,6 +230,8 @@ bool InterfaceEndpointClient::AcceptWithResponder(Message* message,
     return true;
   }
 
+  SyncCallRestrictions::AssertSyncCallAllowed();
+
   bool response_received = false;
   std::unique_ptr<MessageReceiver> sync_responder(responder);
   sync_responses_.insert(std::make_pair(