Reland of Thread maybe-assigned through the bytecodes.

test/cctest/interpreter/bytecode_expectations/ClassDeclarations.golden

 #
 # Autogenerated by generate-bytecode-expectations.
 #
 
 ---
 wrap: yes
 
 ---
 snippet: "
   class Person {
@@ skipping 124 matching lines @@
                 B(Star), R(4),
                 B(LdaTheHole),
                 B(Star), R(5),
                 B(LdaSmi), I8(62),
                 B(Star), R(7),
                 B(Wide), B(LdaSmi), I16(128),
                 B(Star), R(8),
                 B(Mov), R(4), R(6),
                 B(CallRuntime), U16(Runtime::kDefineClass), R(5), U8(4),
                 B(Star), R(5),
-                B(LdaCurrentContextSlot), U8(4),
+                B(LdaImmutableCurrentContextSlot), U8(4),
   /*   75 E> */ B(ToName), R(7),
                 B(CreateClosure), U8(3), U8(3), U8(2),
                 B(Star), R(8),
                 B(LdaSmi), I8(2),
                 B(Star), R(9),
                 B(Ldar), R(8),
                 B(StaDataPropertyInLiteral), R(5), R(7), U8(3), U8(5),
-                B(LdaCurrentContextSlot), U8(5),
+                B(LdaImmutableCurrentContextSlot), U8(5),
   /*  106 E> */ B(ToName), R(7),
                 B(LdaConstant), U8(4),
                 B(TestEqualStrict), R(7), U8(0),
                 B(Mov), R(4), R(6),
                 B(JumpIfToBooleanFalse), U8(7),
                 B(CallRuntime), U16(Runtime::kThrowStaticPrototypeError), R(0), U8(0),
                 B(CreateClosure), U8(5), U8(4), U8(2),
                 B(Star), R(8),
                 B(StaDataPropertyInLiteral), R(6), R(7), U8(3), U8(7),
                 B(CallRuntime), U16(Runtime::kInstallClassNameAccessorWithCheck), R(4), U8(1),
@@ skipping 115 matching lines @@
 ]
 constant pool: [
   SHARED_FUNCTION_INFO_TYPE,
   SHARED_FUNCTION_INFO_TYPE,
   ONE_BYTE_INTERNALIZED_STRING_TYPE ["name"],
   SHARED_FUNCTION_INFO_TYPE,
 ]
 handlers: [
 ]