Use PASS() everywhere in ppapi/tests.

ppapi/tests/test_file_io.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_file_io.h"
 
 #include <stdio.h>
 
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/c/dev/ppb_file_io_dev.h"
@@ skipping 95 matching lines @@
   // Try opening a file that doesn't exist.
   pp::FileRef_Dev nonexistent_file_ref(file_system, "/nonexistent_file");
   pp::FileIO_Dev nonexistent_file_io;
   rv = nonexistent_file_io.Open(
       nonexistent_file_ref, PP_FILEOPENFLAG_READ, callback);
   if (rv == PP_ERROR_WOULDBLOCK)
     rv = callback.WaitForResult();
   if (rv != PP_ERROR_FILENOTFOUND)
     return ReportError("FileIO::Open", rv);
 
-  return "";
+  PASS();
 }
 
 std::string TestFileIO::TestReadWriteSetLength() {
   TestCompletionCallback callback;
 
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   pp::FileRef_Dev file_ref(file_system, "/file_read_write_setlength");
   int32_t rv = file_system.Open(1024, callback);
   if (rv == PP_ERROR_WOULDBLOCK)
     rv = callback.WaitForResult();
@@ skipping 93 matching lines @@
 
   // Read from the middle of the file.
   read_buffer.clear();
   rv = ReadEntireFile(&file_io, 4, &read_buffer);
   if (rv != PP_OK)
     return ReportError("FileIO::Read", rv);
   if (read_buffer != std::string("testtest\0\0\0\0", 12))
     return ReportMismatch("FileIO::Read", read_buffer,
                           std::string("testtest\0\0\0\0", 12));
 
-  return "";
+  PASS();
 }
 
 std::string TestFileIO::TestTouchQuery() {
   TestCompletionCallback callback;
 
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   int32_t rv = file_system.Open(1024, callback);
   if (rv == PP_ERROR_WOULDBLOCK)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ skipping 33 matching lines @@
   if (rv != PP_OK)
     return ReportError("FileSystem::Query", rv);
 
   if ((info.size != 4) ||
       (info.type != PP_FILETYPE_REGULAR) ||
       (info.system_type != PP_FILESYSTEMTYPE_LOCALTEMPORARY) ||
       (info.last_access_time != last_access_time) ||
       (info.last_modified_time != last_modified_time))
     return "FileSystem::Query() has returned bad data.";
 
-  return "";
+  PASS();
 }