Introduce intrinsics for double values in Javascript.

src/runtime.h

Index: src/runtime.h
diff --git a/src/runtime.h b/src/runtime.h
index 823285fd37661bad76a15483a06cc104b680512b..64dccf56337c9e1be151998a1f08951246c6026a 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -189,6 +189,9 @@ namespace internal {
   F(Math_atan2, 2, 1) \
   F(RoundNumber, 1, 1) \
   F(Math_fround, 1, 1) \
+  F(DoubleHi, 1, 1) \
+  F(DoubleLo, 1, 1) \
+  F(ConstructDouble, 2, 1) \
   \
   /* Regular expressions */ \
   F(RegExpCompile, 3, 1) \
@@ -666,7 +669,10 @@ namespace internal {
   F(RegExpExec, 4, 1)                                                        \
   F(RegExpConstructResult, 3, 1)                                             \
   F(GetFromCache, 2, 1)                                                      \
-  F(NumberToString, 1, 1)
+  F(NumberToString, 1, 1)                                                    \
+  F(DoubleHi, 1, 1)                                                          \
+  F(DoubleLo, 1, 1)                                                          \
+  F(ConstructDouble, 2, 1)
 
 
 //---------------------------------------------------------------------------