Partially revert r42319 to pacify tests.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index 956797c49bf934dbaad44a68e0871532cf068a4b..8f2bc4cfc34ed63491cf9b6eb3abe04ec6656b29 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -2065,7 +2065,13 @@ Definition* UnboxIntegerInstr::Canonicalize(FlowGraph* flow_graph) {
           box_defn->value()->CopyWithType(),
           (representation() == kUnboxedInt32) ?
               GetDeoptId() : Isolate::kNoDeoptId);
-      if ((representation() == kUnboxedInt32) && is_truncating()) {
+      // TODO(vegorov): marking resulting converted as truncating when
+      // unboxing can't deoptimize is a work-around missing
+      // deoptimization environment in case when we insert converter after
+      // EliminateEnvironments and there is mismatch between predicates
+      // UnboxIntConverterInstr::CanDeoptimize and UnboxInt32::CanDeoptimize.
+      if ((representation() == kUnboxedInt32) &&
+          (is_truncating() || !CanDeoptimize())) {
         converter->mark_truncating();
       }
       flow_graph->InsertBefore(this, converter, env(), FlowGraph::kValue);