Don't iterate over IC data that may be updated by the mutator thread.

runtime/vm/flow_graph_compiler.cc

Index: runtime/vm/flow_graph_compiler.cc
diff --git a/runtime/vm/flow_graph_compiler.cc b/runtime/vm/flow_graph_compiler.cc
index ae995166ae2f41bdfa14bc580f49a65feb1b533e..93225db913ab93d2e03d6f8a43c062ae478c2da3 100644
--- a/runtime/vm/flow_graph_compiler.cc
+++ b/runtime/vm/flow_graph_compiler.cc
@@ -1194,7 +1194,7 @@ void FlowGraphCompiler::GenerateInstanceCall(
     return;
   }
   ASSERT(!ic_data.IsNull());
-  if (is_optimizing() && (ic_data.NumberOfUsedChecks() == 0)) {
+  if (is_optimizing() && (ic_data_in.NumberOfUsedChecks() == 0)) {
     // Emit IC call that will count and thus may need reoptimization at
     // function entry.
     ASSERT(may_reoptimize() || flow_graph().IsCompiledForOsr());