Use the constant pool for all constants, not just null.

runtime/vm/flow_graph_inliner.cc

Index: runtime/vm/flow_graph_inliner.cc
diff --git a/runtime/vm/flow_graph_inliner.cc b/runtime/vm/flow_graph_inliner.cc
index 32fe75e66da82cda8ad2ef0894a3953d150306dc..f57251c4f20aec27667cec67d2547e309b6dc9f9 100644
--- a/runtime/vm/flow_graph_inliner.cc
+++ b/runtime/vm/flow_graph_inliner.cc
@@ -670,8 +670,7 @@ class CallSiteInliner : public ValueObject {
       ConstantInstr* constant = (*defns)[i]->AsConstant();
       if ((constant != NULL) && constant->HasUses()) {
         constant->ReplaceUsesWith(
-            caller_graph_->AddConstantToInitialDefinitions(
-                constant->value()));
+            caller_graph_->GetConstant(constant->value()));
       }
     }
 
@@ -1027,8 +1026,7 @@ bool PolymorphicInliner::TryInlining(const Function& target) {
     ConstantInstr* constant = (*defns)[i]->AsConstant();
     if ((constant != NULL) && constant->HasUses()) {
       constant->ReplaceUsesWith(
-          owner_->caller_graph()->AddConstantToInitialDefinitions(
-              constant->value()));
+          owner_->caller_graph()->GetConstant(constant->value()));
     }
   }
   return true;