Add visibility restrictions to all mojoms that export symbols.

mojo/public/interfaces/bindings/tests/BUILD.gn

Index: mojo/public/interfaces/bindings/tests/BUILD.gn
diff --git a/mojo/public/interfaces/bindings/tests/BUILD.gn b/mojo/public/interfaces/bindings/tests/BUILD.gn
index d3b964d7003302b30d8bb69b62b9e7ec0af1a0e4..9b10db0064f594f6f9c88c8edabf12881482ab56 100644
--- a/mojo/public/interfaces/bindings/tests/BUILD.gn
+++ b/mojo/public/interfaces/bindings/tests/BUILD.gn
@@ -61,10 +61,10 @@ mojom("test_export") {
     export_header_blink =
         "mojo/public/cpp/bindings/tests/mojo_test_blink_export.h"
   }
-  visibility = [
-    ":test_export_component",
-    ":test_export_blink_component",
-  ]
+  visibility = [ ":test_export_component" ]
+  if (!is_ios) {
+    visibility_blink = [ ":test_export_blink_component" ]
+  }
 }
 
 mojom("test_exported_import") {