Bailout if field state changed during background compilation.

runtime/vm/block_scheduler.cc

Index: runtime/vm/block_scheduler.cc
diff --git a/runtime/vm/block_scheduler.cc b/runtime/vm/block_scheduler.cc
index a84a5d96300b070fb4959b719a97e53a7455fe1e..1288d0b19471820680cc9d5d986f356f6c35b6ea 100644
--- a/runtime/vm/block_scheduler.cc
+++ b/runtime/vm/block_scheduler.cc
@@ -6,6 +6,7 @@
 
 #include "vm/allocation.h"
 #include "vm/code_patcher.h"
+#include "vm/compiler.h"
 #include "vm/flow_graph.h"
 
 namespace dart {
@@ -60,6 +61,11 @@ void BlockScheduler::AssignEdgeWeights() const {
 
   const Array& ic_data_array = Array::Handle(flow_graph()->zone(),
       flow_graph()->parsed_function().function().ic_data_array());
+  if (Compiler::IsBackgroundCompilation() && ic_data_array.IsNull()) {
+    // Deferred loading cleared ic_data_array.
+    Compiler::AbortBackgroundCompilation(Thread::kNoDeoptId);
+  }
+  ASSERT(!ic_data_array.IsNull());
   Array& edge_counters = Array::Handle();
   edge_counters ^= ic_data_array.At(0);