Use mutable heapnumbers to store doubles in fields.

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index 149a6492621aaa0a88dee1c4eb725b7e9331d437..e56a6a31ad2cbb23e8e67988e9250c96bdb62091 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -1508,6 +1508,11 @@ static void Generate_KeyedLoadIC_NonStrictArguments(MacroAssembler* masm) {
   KeyedLoadIC::GenerateNonStrictArguments(masm);
 }
 
+static void Generate_StoreIC_Slow(MacroAssembler* masm) {
+  StoreIC::GenerateSlow(masm);
+}
+
+
 static void Generate_StoreIC_Initialize(MacroAssembler* masm) {
   StoreIC::GenerateInitialize(masm);
 }