Use PASS() everywhere in ppapi/tests.

ppapi/tests/test_url_loader.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_url_loader.h"
 
 #include <stdio.h>
 #include <string>
 
 #include "ppapi/c/dev/ppb_file_io_dev.h"
@@ skipping 224 matching lines @@
   if (data.size() != expected_body.size())
     return "ReadEntireFile returned unexpected content length";
   if (data != expected_body)
     return "ReadEntireFile returned unexpected content";
 
   int32_t file_descriptor = file_io_trusted_interface_->GetOSFileDescriptor(
       reader.pp_resource());
   if (file_descriptor < 0)
     return "FileIO::GetOSFileDescriptor() returned a bad file descriptor.";
 
-  return "";
+  PASS();
 }
 
 std::string TestURLLoader::TestSameOriginRestriction() {
   pp::URLRequestInfo request;
   request.SetURL("http://www.google.com/");
 
   TestCompletionCallback callback;
 
   pp::URLLoader loader(*instance_);
   int32_t rv = loader.Open(request, callback);
   if (rv == PP_ERROR_WOULDBLOCK)
     rv = callback.WaitForResult();
 
   // We expect a failure.
   if (rv != PP_ERROR_NOACCESS) {
     if (rv == PP_OK) {
       return "URLLoader::Open() failed to block a cross-origin request.";
     } else {
       return ReportError("URLLoader::Open()", rv);
     }
   }
 
-  return "";
+  PASS();
 }
 
 // This test should cause a redirect and ensure that the loader runs
 // the callback, rather than following the redirect.
 std::string TestURLLoader::TestAuditURLRedirect() {
   pp::URLRequestInfo request;
   // This path will cause the server to return a 301 redirect.
   request.SetURL("/server-redirect?www.google.com");
   request.SetFollowRedirects(false);
 
@@ skipping 14 matching lines @@
   int32_t status_code = response_info.GetStatusCode();
   if (status_code != 301)
     return "Response status should be 301";
   if (response_info.GetRedirectURL().AsString() != "www.google.com")
     return "Redirect URL should be www.google.com";
 
   return "";
 }
 
 // TODO(darin): Add a test for GrantUniversalAccess.