[turbofan] Add support for transitioning stores to double fields.

src/code-stubs-hydrogen.cc

Index: src/code-stubs-hydrogen.cc
diff --git a/src/code-stubs-hydrogen.cc b/src/code-stubs-hydrogen.cc
index 60e626e1aec843a4a04b0fc418a9dec6e5aa75e5..8ec255b2644fff2329f069941e231cec3bb03fdc 100644
--- a/src/code-stubs-hydrogen.cc
+++ b/src/code-stubs-hydrogen.cc
@@ -1141,6 +1141,21 @@ Handle<Code> AllocateHeapNumberStub::GenerateCode() {
 
 
 template <>
+HValue* CodeStubGraphBuilder<AllocateMutableHeapNumberStub>::BuildCodeStub() {
+  HValue* result =
+      Add<HAllocate>(Add<HConstant>(HeapNumber::kSize), HType::HeapObject(),
+                     NOT_TENURED, MUTABLE_HEAP_NUMBER_TYPE);
+  AddStoreMapConstant(result, isolate()->factory()->mutable_heap_number_map());
+  return result;
+}
+
+
+Handle<Code> AllocateMutableHeapNumberStub::GenerateCode() {
+  return DoGenerateCode(this);
+}
+
+
+template <>
 HValue* CodeStubGraphBuilder<AllocateInNewSpaceStub>::BuildCodeStub() {
   HValue* result = Add<HAllocate>(GetParameter(0), HType::Tagged(), NOT_TENURED,
                                   JS_OBJECT_TYPE);