Move ConstantPropagator from flow_graph_optimizer.cc/.h into separate files.

runtime/vm/vm_sources.gypi

 # Copyright (c) 2013, 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 77 matching lines @@
     'code_patcher_ia32_test.cc',
     'code_patcher_mips.cc',
     'code_patcher_mips_test.cc',
     'code_patcher_x64.cc',
     'code_patcher_x64_test.cc',
     'compiler.cc',
     'compiler.h',
     'compiler_stats.cc',
     'compiler_stats.h',
     'compiler_test.cc',
+    'constant_propagator.h',
+    'constant_propagator.cc',
     'constants_arm.h',
     'constants_arm64.h',
     'constants_ia32.h',
     'constants_mips.h',
     'constants_x64.h',
     'counters.cc',
     'counters.h',
     'coverage.cc',
     'coverage.h',
     'coverage_test.cc',
@@ skipping 357 matching lines @@
     'vtune.h',
     'weak_code.cc',
     'weak_code.h',
     'weak_table.cc',
     'weak_table.h',
     'zone.cc',
     'zone.h',
     'zone_test.cc',
   ],
 }