Fix LoadFieldByIndex to take mutable heap-numbers into account.

src/runtime.h

 // 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 82 matching lines @@
   F(GetOptimizationCount, 1, 1) \
   F(UnblockConcurrentRecompilation, 0, 1) \
   F(CompileForOnStackReplacement, 1, 1) \
   F(SetAllocationTimeout, -1 /* 2 || 3 */, 1) \
   F(SetNativeFlag, 1, 1) \
   F(SetInlineBuiltinFlag, 1, 1) \
   F(StoreArrayLiteralElement, 5, 1) \
   F(DebugCallbackSupportsStepping, 1, 1) \
   F(DebugPrepareStepInIfStepping, 1, 1) \
   F(FlattenString, 1, 1) \
+  F(LoadMutableDouble, 2, 1) \
   F(TryMigrateInstance, 1, 1) \
   F(NotifyContextDisposed, 0, 1) \
   \
   /* Array join support */ \
   F(PushIfAbsent, 2, 1) \
   F(ArrayConcat, 1, 1) \
   \
   /* Conversions */ \
   F(ToBool, 1, 1) \
   F(Typeof, 1, 1) \
@@ skipping 797 matching lines @@
 class AllocateDoubleAlignFlag:  public BitField<bool,            0, 1> {};
 class AllocateTargetSpace:      public BitField<AllocationSpace, 1, 3> {};
 
 class DeclareGlobalsEvalFlag:   public BitField<bool,       0, 1> {};
 class DeclareGlobalsNativeFlag: public BitField<bool,       1, 1> {};
 class DeclareGlobalsStrictMode: public BitField<StrictMode, 2, 1> {};
 
 } }  // namespace v8::internal
 
 #endif  // V8_RUNTIME_H_