Record field initializer stores with simple literals at compile-time.

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
===================================================================
--- runtime/vm/intermediate_language_ia32.cc	(revision 37262)
+++ runtime/vm/intermediate_language_ia32.cc	(working copy)
@@ -1739,8 +1739,8 @@
           ((IsPotentialUnboxedStore()) ? 3 : 0);
   LocationSummary* summary = new(isolate) LocationSummary(
       isolate, kNumInputs, kNumTemps,
-          !field().IsNull() &&
-          ((field().guarded_cid() == kIllegalCid) || is_initialization_)
+          ((IsUnboxedStore() && opt && is_initialization_) ||
+           IsPotentialUnboxedStore())
           ? LocationSummary::kCallOnSlowPath
           : LocationSummary::kNoCall);
 
@@ -1830,6 +1830,7 @@
   }
 
   if (IsPotentialUnboxedStore()) {
+    __ Comment("PotentialUnboxedStore");
     Register value_reg = locs()->in(1).reg();
     Register temp = locs()->temp(0).reg();
     Register temp2 = locs()->temp(1).reg();