Introduce LanguageMode, drop StrictMode.

src/execution.cc

 // Copyright 2014 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/execution.h"
 
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
 #include "src/deoptimizer.h"
 #include "src/isolate-inl.h"
@@ skipping 148 matching lines @@
                                     Handle<Object> argv[],
                                     bool convert_receiver) {
   if (!callable->IsJSFunction()) {
     ASSIGN_RETURN_ON_EXCEPTION(
         isolate, callable, TryGetFunctionDelegate(isolate, callable), Object);
   }
   Handle<JSFunction> func = Handle<JSFunction>::cast(callable);
 
   // In sloppy mode, convert receiver.
   if (convert_receiver && !receiver->IsJSReceiver() &&
-      !func->shared()->native() &&
-      func->shared()->strict_mode() == SLOPPY) {
+      !func->shared()->native() && is_sloppy(func->shared()->language_mode())) {
     if (receiver->IsUndefined() || receiver->IsNull()) {
       receiver = handle(func->global_proxy());
       DCHECK(!receiver->IsJSBuiltinsObject());
     } else {
       ASSIGN_RETURN_ON_EXCEPTION(
           isolate, receiver, ToObject(isolate, receiver), Object);
     }
   }
 
   return Invoke(false, func, receiver, argc, argv);
@@ skipping 564 matching lines @@
   }
 
   isolate_->counters()->stack_interrupts()->Increment();
   isolate_->counters()->runtime_profiler_ticks()->Increment();
   isolate_->runtime_profiler()->OptimizeNow();
 
   return isolate_->heap()->undefined_value();
 }
 
 } }  // namespace v8::internal