Don't run the second pass of the pending phantom callbacks if the heap has been torn down.

BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/mips.gni")
 
 # Because standalone V8 builds are not supported, assume this is part of a
 # Chromium build.
@@ skipping 612 matching lines @@
     "src/bignum-dtoa.h",
     "src/bignum.cc",
     "src/bignum.h",
     "src/bit-vector.cc",
     "src/bit-vector.h",
     "src/bootstrapper.cc",
     "src/bootstrapper.h",
     "src/builtins.cc",
     "src/builtins.h",
     "src/bytecodes-irregexp.h",
+    "src/cancelable-task.cc",
+    "src/cancelable-task.h",
     "src/cached-powers.cc",
     "src/cached-powers.h",
     "src/char-predicates.cc",
     "src/char-predicates-inl.h",
     "src/char-predicates.h",
     "src/checks.cc",
     "src/checks.h",
     "src/circular-queue-inl.h",
     "src/circular-queue.h",
     "src/code-factory.cc",
@@ skipping 1118 matching lines @@
         "src/d8-debug.cc",
         "src/d8-debug.h",
         "$target_gen_dir/d8-js.cc",
       ]
     }
     if (v8_enable_i18n_support) {
       deps += [ "//third_party/icu" ]
     }
   }
 }