Re-land http://codereview.chromium.org/9403039/, r124106

ppapi/tests/testing_instance.h

Index: ppapi/tests/testing_instance.h
diff --git a/ppapi/tests/testing_instance.h b/ppapi/tests/testing_instance.h
index 8dadb20861094b90ef6aabecf854fc21cf93ceb2..701c5ca03b27ea786481f4997d5c93e964ff947c 100644
--- a/ppapi/tests/testing_instance.h
+++ b/ppapi/tests/testing_instance.h
@@ -92,6 +92,11 @@ pp::InstancePrivate {
 
   void ReportProgress(const std::string& progress_value);
 
+  // Add a post-condition to the JavaScript on the test_case.html page. This
+  // JavaScript code will be run after the instance is shut down and must
+  // evaluate to |true| or the test will fail.
+  void AddPostCondition(const std::string& script);
+
  private:
   void ExecuteTests(int32_t unused);
 
@@ -109,6 +114,10 @@ pp::InstancePrivate {
   // Runs 'PostMessage_SendingData.
   std::string FilterForTestName(const std::string& name);
 
+  // Sends a test command to the page using PostMessage.
+  void SendTestCommand(const std::string& command);
+  void SendTestCommand(const std::string& command, const std::string& params);
+
   // Appends a list of available tests to the console in the document.
   void LogAvailableTests();