Add TestingInstance::EvalScript method which posts a message that the test page can eval().

ppapi/tests/testing_instance.cc

Index: ppapi/tests/testing_instance.cc
===================================================================
--- ppapi/tests/testing_instance.cc	(revision 114869)
+++ ppapi/tests/testing_instance.cc	(working copy)
@@ -101,6 +101,12 @@
   return false;
 }
 
+void TestingInstance::EvalScript(const std::string& script) {
+  std::string message("TESTING_MESSAGE:EvalScript:");
+  message.append(script);
+  PostMessage(pp::Var(message));
+}
+
 void TestingInstance::LogTest(const std::string& test_name,
                               const std::string& error_message) {
   // Tell the browser we're still working.