Add a mid-sized integration test for the Dart Embedding Api which

runtime/vm/vm_sources.gypi

 # Copyright (c) 2011, 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 53 matching lines @@
     'compiler_stats.cc',
     'compiler_test.cc',
     'constants_ia32.h',
     'constants_x64.h',
     'constants_arm.h',
     'cpu.h',
     'cpu_ia32.cc',
     'cpu_x64.cc',
     'cpu_arm.cc',
     'cpu_test.cc',
+    'custom_isolate_test.cc',
     'dart.cc',
     'dart.h',
     'dart_api_impl.h',
     'dart_api_state.cc',
     'dart_api_state.h',
     'dart_api_impl_test.cc',
     'dart_entry.cc',
     'dart_entry.h',
     'dart_entry_test.cc',
     'disassembler.cc',
@@ skipping 155 matching lines @@
     'virtual_memory_test.cc',
     'virtual_memory_win.cc',
     'verifier.cc',
     'verifier.h',
     'visitor.h',
     'zone.cc',
     'zone.h',
     'zone_test.cc',
   ],
 }