Turn dead code elimination into a proper HPhase.

tools/gyp/v8.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 317 matching lines @@
         '../../src/handles.h',
         '../../src/hashmap.h',
         '../../src/heap-inl.h',
         '../../src/heap-profiler.cc',
         '../../src/heap-profiler.h',
         '../../src/heap-snapshot-generator-inl.h',
         '../../src/heap-snapshot-generator.cc',
         '../../src/heap-snapshot-generator.h',
         '../../src/heap.cc',
         '../../src/heap.h',
+        '../../src/hydrogen-dce.cc',
+        '../../src/hydrogen-dce.h',
         '../../src/hydrogen-environment-liveness.cc',
         '../../src/hydrogen-environment-liveness.h',
         '../../src/hydrogen-escape-analysis.cc',
         '../../src/hydrogen-escape-analysis.h',
         '../../src/hydrogen-instructions.cc',
         '../../src/hydrogen-instructions.h',
         '../../src/hydrogen.cc',
         '../../src/hydrogen.h',
         '../../src/hydrogen-gvn.cc',
         '../../src/hydrogen-gvn.h',
@@ skipping 655 matching lines @@
         }],
         ['v8_compress_startup_data=="bz2"', {
           'libraries': [
             '-lbz2',
           ]
         }],
       ],
     },
   ],
 }