Split ToDouble into two IL instruction to make it work with SSA.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
===================================================================
--- runtime/vm/intermediate_language.cc	(revision 10708)
+++ runtime/vm/intermediate_language.cc	(working copy)
@@ -833,11 +833,16 @@
 }
 
 
-RawAbstractType* ToDoubleComp::CompileType() const {
+RawAbstractType* DoubleToDoubleComp::CompileType() const {
   return Type::DoubleInterface();
 }
 
 
+RawAbstractType* SmiToDoubleComp::CompileType() const {
+  return Type::DoubleInterface();
+}
+
+
 // Shared code generation methods (EmitNativeCode, MakeLocationSummary, and
 // PrepareEntry). Only assembly code that can be shared across all architectures
 // can be used. Machine specific register allocation and code generation