Porting r9456 to x64 (Optimize KeyedStoreGeneric for Smi arrays).

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index db827854ef4695f1fd6f97f6d330e371ea4bf8bd..7e0ba00546c167988f97f6daa3411cc075d7c984 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -859,6 +859,16 @@ class MacroAssembler: public Assembler {
                                 Label* fail,
                                 Label::Distance distance = Label::kFar);
 
+  // Check to see if maybe_number can be stored as a double in
+  // FastDoubleElements. If it can, store it at the index specified by key in
+  // the FastDoubleElements array elements, otherwise jump to fail.
+  // Note that key must not be smi-tagged.
+  void StoreNumberToDoubleElements(Register maybe_number,
+                                   Register elements,
+                                   Register key,
+                                   XMMRegister xmm_scratch,
+                                   Label* fail);
+
   // Check if the map of an object is equal to a specified map and
   // branch to label if not. Skip the smi check if not required
   // (object is known to be a heap object)