Don't send PP_Vars/V8 values with cycles across PostMessage

ppapi/tests/test_post_message.h

Index: ppapi/tests/test_post_message.h
diff --git a/ppapi/tests/test_post_message.h b/ppapi/tests/test_post_message.h
index 3ea69e898b382d064bb718a23cb787246cbc3097..2f2f6287c087d4cab70a64505ddc4f1bb9964334 100644
--- a/ppapi/tests/test_post_message.h
+++ b/ppapi/tests/test_post_message.h
@@ -34,6 +34,10 @@ class TestPostMessage : public TestCase {
   // Returns true on success, false on failure.
   bool AddEchoingListener(const std::string& expression);
 
+  // Posts a message from JavaScript to the plugin. |func| should be a
+  // JavaScript function which returns the variable to post.
+  bool PostMessageFromJavaScript(const std::string& func);
+
   // Clear any listeners that have been added using AddEchoingListener by
   // calling removeEventListener for each.
   // Returns true on success, false on failure.