[Interpreter] Add a simple dead-code elimination bytecode optimizer.

test/unittests/BUILD.gn

 # Copyright 2016 The V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Please keep this file in sync with unittests.gyp.
 
 import("../../gni/v8.gni")
 
 v8_executable("unittests") {
   testonly = true
@@ skipping 72 matching lines @@
     "heap/bitmap-unittest.cc",
     "heap/gc-idle-time-handler-unittest.cc",
     "heap/gc-tracer-unittest.cc",
     "heap/heap-unittest.cc",
     "heap/memory-reducer-unittest.cc",
     "heap/scavenge-job-unittest.cc",
     "heap/slot-set-unittest.cc",
     "interpreter/bytecode-array-builder-unittest.cc",
     "interpreter/bytecode-array-iterator-unittest.cc",
     "interpreter/bytecode-array-writer-unittest.cc",
+    "interpreter/bytecode-dead-code-optimizer-unittest.cc",
     "interpreter/bytecode-peephole-optimizer-unittest.cc",
     "interpreter/bytecode-pipeline-unittest.cc",
     "interpreter/bytecode-register-allocator-unittest.cc",
     "interpreter/bytecode-register-optimizer-unittest.cc",
     "interpreter/bytecodes-unittest.cc",
     "interpreter/constant-array-builder-unittest.cc",
     "interpreter/interpreter-assembler-unittest.cc",
     "interpreter/interpreter-assembler-unittest.h",
     "interpreter/source-position-table-unittest.cc",
     "libplatform/default-platform-unittest.cc",
@@ skipping 67 matching lines @@
 
     # Suppress warnings about importing locally defined symbols.
     if (is_component_build) {
       ldflags = [
         "/ignore:4049",
         "/ignore:4217",
       ]
     }
   }
 }