Remove unmarked entries from per context map caches.

src/contexts.h

 // Copyright 2011 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 207 matching lines @@
     FUNCTION_CACHE_INDEX,
     JSFUNCTION_RESULT_CACHES_INDEX,
     NORMALIZED_MAP_CACHE_INDEX,
     RUNTIME_CONTEXT_INDEX,
     CALL_AS_FUNCTION_DELEGATE_INDEX,
     CALL_AS_CONSTRUCTOR_DELEGATE_INDEX,
     SCRIPT_FUNCTION_INDEX,
     OPAQUE_REFERENCE_FUNCTION_INDEX,
     CONTEXT_EXTENSION_FUNCTION_INDEX,
     OUT_OF_MEMORY_INDEX,
-    MAP_CACHE_INDEX,
     CONTEXT_DATA_INDEX,
     ALLOW_CODE_GEN_FROM_STRINGS_INDEX,
     DERIVED_GET_TRAP_INDEX,
     DERIVED_SET_TRAP_INDEX,
 
     // Properties from here are treated as weak references by the full GC.
     // Scavenge treats them as strong references.
     OPTIMIZED_FUNCTIONS_LIST,  // Weak.
+    MAP_CACHE_INDEX,  // Weak.
     NEXT_CONTEXT_LINK,  // Weak.
 
     // Total number of slots.
     GLOBAL_CONTEXT_SLOTS,
 
     FIRST_WEAK_SLOT = OPTIMIZED_FUNCTIONS_LIST
   };
 
   // Direct slot access.
   JSFunction* closure() { return JSFunction::cast(get(CLOSURE_INDEX)); }
@@ skipping 138 matching lines @@
 #ifdef DEBUG
   // Bootstrapping-aware type checks.
   static bool IsBootstrappingOrContext(Object* object);
   static bool IsBootstrappingOrGlobalObject(Object* object);
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONTEXTS_H_