Fix CompilerStats aggregation: do not aggregate if there is no mutator thread (isolate shutting dow…

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
diff --git a/runtime/vm/compiler.cc b/runtime/vm/compiler.cc
index 92c3d68f3c69c4292e80586d03c19b1117ca946a..cd6208852615f9181c49291e4170cd94a473c42b 100644
--- a/runtime/vm/compiler.cc
+++ b/runtime/vm/compiler.cc
@@ -1688,7 +1688,10 @@ void BackgroundCompiler::Run() {
         // unoptimized code. Any issues while optimizing are flagged by
         // making the result invalid.
         ASSERT(error.IsNull());
-        isolate->aggregate_compiler_stats()->Add(*thread->compiler_stats());
+        // We cannot aggregate stats if isolate is shutting down.
+        if (isolate->HasMutatorThread()) {
+          isolate->aggregate_compiler_stats()->Add(*thread->compiler_stats());
+        }
         thread->compiler_stats()->Clear();
         QueueElement* qelem = function_queue()->Remove();
         delete qelem;