PPAPI: Compile out thread checks when pepper threading is turned on.

ppapi/shared_impl/var_tracker.h

Index: ppapi/shared_impl/var_tracker.h
diff --git a/ppapi/shared_impl/var_tracker.h b/ppapi/shared_impl/var_tracker.h
index 4df24445833daadfedbdb3740ebc74f81de58e13..94b88834f341e55b960d78ffc1b27dff07a4f689 100644
--- a/ppapi/shared_impl/var_tracker.h
+++ b/ppapi/shared_impl/var_tracker.h
@@ -32,8 +32,12 @@ class Var;
 // This class maintains the "track_with_no_reference_count" but doesn't do
 // anything with it other than call virtual functions. The interesting parts
 // are added by the PluginObjectVar derived from this class.
+#ifdef ENABLE_PEPPER_THREADING
+class PPAPI_SHARED_EXPORT VarTracker {
+#else
 class PPAPI_SHARED_EXPORT VarTracker
     : NON_EXPORTED_BASE(public base::NonThreadSafe) {
+#endif
  public:
   VarTracker();
   virtual ~VarTracker();