Remember deopt-id -> context-level mappings in var descriptors.

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 d0d9d3e6cf596c7b768abc29f7e8fbe69044f4d0..b5063f899d1e8ad245a70bab8a5af522d16385fd 100644
--- a/runtime/vm/flow_graph_inliner.cc
+++ b/runtime/vm/flow_graph_inliner.cc
@@ -800,7 +800,8 @@ class CallSiteInliner : public ValueObject {
               parsed_function->function().kernel_function());
 
           kernel::FlowGraphBuilder builder(
-              node, parsed_function, *ic_data_array, exit_collector,
+              node, parsed_function, *ic_data_array,
+              /* not building var desc */ NULL, exit_collector,
               Compiler::kNoOSRDeoptId, caller_graph_->max_block_id() + 1);
           {
             CSTAT_TIMER_SCOPE(thread(), graphinliner_build_timer);
@@ -808,6 +809,7 @@ class CallSiteInliner : public ValueObject {
           }
         } else {
           FlowGraphBuilder builder(*parsed_function, *ic_data_array,
+                                   /* not building var desc */ NULL,
                                    exit_collector, Compiler::kNoOSRDeoptId);
           builder.SetInitialBlockId(caller_graph_->max_block_id());
           {