Optimize the typeof operator.

src/code-stubs.h

Index: src/code-stubs.h
diff --git a/src/code-stubs.h b/src/code-stubs.h
index c40bc857cad53b1d03778940c7615c3cc67c2a38..bf3619b0a81c5c6caa78fa947eef61cf46793f64 100644
--- a/src/code-stubs.h
+++ b/src/code-stubs.h
@@ -79,6 +79,7 @@ namespace internal {
   V(MegamorphicLoad)                        \
   V(NameDictionaryLookup)                   \
   V(NumberToString)                         \
+  V(Typeof)                                 \
   V(RegExpConstructResult)                  \
   V(StoreFastElement)                       \
   V(StoreScriptContextField)                \
@@ -594,6 +595,20 @@ class NumberToStringStub final : public HydrogenCodeStub {
 };
 
 
+class TypeofStub final : public HydrogenCodeStub {
+ public:
+  explicit TypeofStub(Isolate* isolate) : HydrogenCodeStub(isolate) {}
+
+  // Parameters accessed via CodeStubGraphBuilder::GetParameter()
+  static const int kObject = 0;
+
+  static void GenerateAheadOfTime(Isolate* isolate);
+
+  DEFINE_CALL_INTERFACE_DESCRIPTOR(Typeof);
+  DEFINE_HYDROGEN_CODE_STUB(Typeof, HydrogenCodeStub);
+};
+
+
 class FastNewClosureStub : public HydrogenCodeStub {
  public:
   FastNewClosureStub(Isolate* isolate, LanguageMode language_mode,