Explicitly initialize Code::builtin_index

src/objects.h

 // Copyright 2015 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.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 #include <memory>
 
@@ skipping 5152 matching lines @@
   // level of loop nesting we are willing to do on-stack replacement
   // for.
   inline void set_allow_osr_at_loop_nesting_level(int level);
   inline int allow_osr_at_loop_nesting_level();
 
   // [profiler_ticks]: For FUNCTION kind, tells for how many profiler ticks
   // the code object was seen on the stack with no IC patching going on.
   inline int profiler_ticks();
   inline void set_profiler_ticks(int ticks);
 
-  // [builtin_index]: For BUILTIN kind, tells which builtin index it has.
-  // For builtins, tells which builtin index it has.
-  // Note that builtins can have a code kind other than BUILTIN, which means
-  // that for arbitrary code objects, this index value may be random garbage.
-  // To verify in that case, compare the code object to the indexed builtin.
+  // [builtin_index]: For builtins, tells which builtin index the code object
+  // has. Note that builtins can have a code kind other than BUILTIN. The
+  // builtin index is a non-negative integer for builtins, and -1 otherwise.
   inline int builtin_index();
   inline void set_builtin_index(int id);
 
   // [stack_slots]: For kind OPTIMIZED_FUNCTION, the number of stack slots
   // reserved in the code prologue.
   inline unsigned stack_slots();
   inline void set_stack_slots(unsigned slots);
 
   // [safepoint_table_start]: For kind OPTIMIZED_FUNCTION, the offset in
   // the instruction stream where the safepoint table starts.
@@ skipping 5893 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_