There are only 2 language modes, not 3

src/objects.cc

 // 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.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 9133 matching lines @@
 
 
 Handle<Map> Map::AsLanguageMode(Handle<Map> initial_map,
                                 LanguageMode language_mode, FunctionKind kind) {
   DCHECK_EQ(JS_FUNCTION_TYPE, initial_map->instance_type());
   // Initial map for sloppy mode function is stored in the function
   // constructor. Initial maps for strict mode are cached as special transitions
   // using |strict_function_transition_symbol| as a key.
   if (language_mode == SLOPPY) return initial_map;
   Isolate* isolate = initial_map->GetIsolate();
-  Factory* factory = isolate->factory();
-  Handle<Symbol> transition_symbol;
 
   int map_index = Context::FunctionMapIndex(language_mode, kind);
   Handle<Map> function_map(
       Map::cast(isolate->native_context()->get(map_index)));
 
-  STATIC_ASSERT(LANGUAGE_END == 3);
-  switch (language_mode) {
-    case STRICT:
-      transition_symbol = factory->strict_function_transition_symbol();
-      break;
-    default:
-      UNREACHABLE();
-      break;
-  }
+  STATIC_ASSERT(LANGUAGE_END == 2);
+  DCHECK_EQ(STRICT, language_mode);
+  Handle<Symbol> transition_symbol =
+      isolate->factory()->strict_function_transition_symbol();
   Map* maybe_transition =
       TransitionArray::SearchSpecial(*initial_map, *transition_symbol);
   if (maybe_transition != NULL) {
     return handle(maybe_transition, isolate);
   }
   initial_map->NotifyLeafMapLayoutChange();
 
   // Create new map taking descriptors from the |function_map| and all
   // the other details from the |initial_map|.
   Handle<Map> map =
@@ skipping 7431 matching lines @@
                                          int scope_position) {
     uint32_t hash = source->Hash();
     if (shared->HasSourceCode()) {
       // Instead of using the SharedFunctionInfo pointer in the hash
       // code computation, we use a combination of the hash of the
       // script source code and the start position of the calling scope.
       // We do this to ensure that the cache entries can survive garbage
       // collection.
       Script* script(Script::cast(shared->script()));
       hash ^= String::cast(script->source())->Hash();
-      STATIC_ASSERT(LANGUAGE_END == 3);
+      STATIC_ASSERT(LANGUAGE_END == 2);
       if (is_strict(language_mode)) hash ^= 0x8000;
       hash += scope_position;
     }
     return hash;
   }
 
   uint32_t Hash() override {
     return StringSharedHashHelper(*source_, *shared_, language_mode_,
                                   scope_position_);
   }
@@ skipping 3242 matching lines @@
   for (PrototypeIterator iter(isolate, this, kStartAtReceiver,
                               PrototypeIterator::END_AT_NULL);
        !iter.IsAtEnd(); iter.AdvanceIgnoringProxies()) {
     if (iter.GetCurrent<Object>()->IsJSProxy()) return true;
   }
   return false;
 }
 
 }  // namespace internal
 }  // namespace v8