PPAPI: Dial back the PostMessage threading test and re-enable on Win

ppapi/tests/test_post_message.cc

Index: ppapi/tests/test_post_message.cc
diff --git a/ppapi/tests/test_post_message.cc b/ppapi/tests/test_post_message.cc
index 94b47de48ceeed22fc84aea8ecaf6ec4620848a3..68fe6335cd79423d93556d5a4fb1e0a06521249e 100644
--- a/ppapi/tests/test_post_message.cc
+++ b/ppapi/tests/test_post_message.cc
@@ -29,8 +29,16 @@ const char kTestString[] = "Hello world!";
 const bool kTestBool = true;
 const int32_t kTestInt = 42;
 const double kTestDouble = 42.0;
+
+// On Windows XP bots, the NonMainThread test can run very slowly. So we dial
+// back the number of threads & messages when running on Windows.
+#ifdef PPAPI_OS_WIN
+const int32_t kThreadsToRun = 2;
+const int32_t kMessagesToSendPerThread = 5;
+#else
 const int32_t kThreadsToRun = 4;
 const int32_t kMessagesToSendPerThread = 10;
+#endif
 
 // The struct that invoke_post_message_thread_func expects for its argument.
 // It includes the instance on which to invoke PostMessage, and the value to