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..9ab22f2d02a00a3aac785473cbcd82562efe3dab 100644
--- a/ppapi/shared_impl/var_tracker.h
+++ b/ppapi/shared_impl/var_tracker.h
@@ -33,7 +33,13 @@ class Var;
 // anything with it other than call virtual functions. The interesting parts
 // are added by the PluginObjectVar derived from this class.
 class PPAPI_SHARED_EXPORT VarTracker
+#ifdef ENABLE_PEPPER_THREADING
+    : NON_EXPORTED_BASE(public base::NonThreadSafeDoNothing) {
+#else
+    // TODO(dmichael): Remove the thread checking when calls are allowed off the
+    // main thread (crbug.com/92909).
     : NON_EXPORTED_BASE(public base::NonThreadSafe) {
+#endif
  public:
   VarTracker();
   virtual ~VarTracker();