Use PASS() everywhere in ppapi/tests.

ppapi/tests/test_instance_deprecated.cc

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ppapi/tests/test_instance_deprecated.h"
 
 #include "ppapi/cpp/module.h"
 #include "ppapi/cpp/dev/scriptable_object_deprecated.h"
 #include "ppapi/tests/testing_instance.h"
 
@@ skipping 100 matching lines @@
   // TODO(brettw) bug 54011: The TryCatch isn't working properly and
   // doesn't actually pass the exception text up.
   //ASSERT_TRUE(exception.AsString() == "plugin exception");
 
   // Exception caused by string evaluation should be caught.
   exception = pp::Var();
   ret = instance_->ExecuteScript("document.doesntExist()", &exception);
   ASSERT_TRUE(ret.is_undefined());
   ASSERT_TRUE(exception.is_string());  // Don't know exactly what it will say.
 
-  return std::string();
+  PASS();
 }