Add an API to pump the message loop to libplatform

test/cctest/cctest.gyp

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 67 matching lines @@
         'test-fixed-dtoa.cc',
         'test-flags.cc',
         'test-func-name-inference.cc',
         'test-global-handles.cc',
         'test-global-object.cc',
         'test-hashing.cc',
         'test-hashmap.cc',
         'test-heap.cc',
         'test-heap-profiler.cc',
         'test-hydrogen-types.cc',
+        'test-libplatform-default-platform.cc',
         'test-libplatform-task-queue.cc',
         'test-libplatform-worker-thread.cc',
         'test-list.cc',
         'test-liveedit.cc',
         'test-lockers.cc',
         'test-log.cc',
         'test-microtask-delivery.cc',
         'test-mark-compact.cc',
         'test-mementos.cc',
         'test-mutex.cc',
@@ skipping 161 matching lines @@
             '<@(_outputs)',
             'TEST',  # type
             'off',  # compression
             '<@(file_list)',
           ],
         }
       ],
     },
   ],
 }