Move Mutex and Monitor from vm/ to platform/

runtime/vm/vm_sources.gypi

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # This file contains all sources (vm and tests) for the dart virtual machine.
 # Unit test files need to have a '_test' suffix appended to the name.
 {
   'sources': [
     'allocation.cc',
     'allocation.h',
@@ skipping 216 matching lines @@
     'store_buffer.cc',
     'store_buffer.h',
     'stub_code.cc',
     'stub_code.h',
     'stub_code_arm.cc',
     'stub_code_ia32.cc',
     'stub_code_ia32_test.cc',
     'stub_code_x64.cc',
     'stub_code_x64_test.cc',
     'thread.h',
-    'thread_linux.cc',
-    'thread_linux.h',
-    'thread_macos.cc',
-    'thread_macos.h',
     'thread_test.cc',
-    'thread_win.cc',
-    'thread_win.h',
     'timer.cc',
     'timer.h',
     'token.cc',
     'token.h',
     'unicode.cc',
     'unicode.h',
     'unicode_data.cc',
     'unicode_test.cc',
     'unit_test.cc',
     'unit_test.h',
     'utils_test.cc',
     'virtual_memory.cc',
     'virtual_memory.h',
     'virtual_memory_linux.cc',
     'virtual_memory_macos.cc',
     'virtual_memory_test.cc',
     'virtual_memory_win.cc',
     'verifier.cc',
     'verifier.h',
     'visitor.h',
     'zone.cc',
     'zone.h',
     'zone_test.cc',
   ],
 }