Make setting length on arrays faster.

src/ic.h

Index: src/ic.h
diff --git a/src/ic.h b/src/ic.h
index feff8c5b6e947855f51e5a66598d193cf8ed3b49..d545989bf6c0f610b48ec3a1814dbec5869fd59b 100644
--- a/src/ic.h
+++ b/src/ic.h
@@ -45,6 +45,7 @@ enum DictionaryCheck { CHECK_DICTIONARY, DICTIONARY_CHECK_DONE };
   ICU(KeyedLoadIC_Miss)                               \
   ICU(CallIC_Miss)                                    \
   ICU(StoreIC_Miss)                                   \
+  ICU(StoreIC_ArrayLength)                            \
   ICU(SharedStoreIC_ExtendStorage)                    \
   ICU(KeyedStoreIC_Miss)                              \
   /* Utilities for IC stubs. */                       \
@@ -358,6 +359,7 @@ class StoreIC: public IC {
   static void GenerateInitialize(MacroAssembler* masm) { GenerateMiss(masm); }
   static void GenerateMiss(MacroAssembler* masm);
   static void GenerateMegamorphic(MacroAssembler* masm);
+  static void GenerateArrayLength(MacroAssembler* masm);
 
  private:
   // Update the inline cache and the global stub cache based on the