Introduce LanguageMode, drop StrictMode.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index ae1822372fe85306740f7df0290206717f99de3a..ff128605e6618bf7b215e321ee82af04d5b35f30 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -128,8 +128,7 @@ bool LCodeGen::GeneratePrologue() {
 
     // Sloppy mode functions need to replace the receiver with the global proxy
     // when called as functions (without an explicit receiver object).
-    if (info_->this_has_uses() &&
-        info_->strict_mode() == SLOPPY &&
+    if (info_->this_has_uses() && is_sloppy(info_->language_mode()) &&
         !info_->is_native()) {
       Label ok;
       StackArgumentsAccessor args(rsp, scope()->num_parameters());
@@ -4271,7 +4270,7 @@ void LCodeGen::DoStoreNamedGeneric(LStoreNamedGeneric* instr) {
   DCHECK(ToRegister(instr->value()).is(StoreDescriptor::ValueRegister()));
 
   __ Move(StoreDescriptor::NameRegister(), instr->hydrogen()->name());
-  Handle<Code> ic = StoreIC::initialize_stub(isolate(), instr->strict_mode());
+  Handle<Code> ic = StoreIC::initialize_stub(isolate(), instr->language_mode());
   CallCode(ic, RelocInfo::CODE_TARGET, instr);
 }
 
@@ -4531,7 +4530,7 @@ void LCodeGen::DoStoreKeyedGeneric(LStoreKeyedGeneric* instr) {
   DCHECK(ToRegister(instr->value()).is(StoreDescriptor::ValueRegister()));
 
   Handle<Code> ic =
-      CodeFactory::KeyedStoreIC(isolate(), instr->strict_mode()).code();
+      CodeFactory::KeyedStoreIC(isolate(), instr->language_mode()).code();
   CallCode(ic, RelocInfo::CODE_TARGET, instr);
 }
 
@@ -5515,7 +5514,7 @@ void LCodeGen::DoFunctionLiteral(LFunctionLiteral* instr) {
   // space for nested functions that don't need literals cloning.
   bool pretenure = instr->hydrogen()->pretenure();
   if (!pretenure && instr->hydrogen()->has_no_literals()) {
-    FastNewClosureStub stub(isolate(), instr->hydrogen()->strict_mode(),
+    FastNewClosureStub stub(isolate(), instr->hydrogen()->language_mode(),
                             instr->hydrogen()->kind());
     __ Move(rbx, instr->hydrogen()->shared_info());
     CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);