Invalidate background compilation only if relevant fields were invalidated.

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index e1564da5f24cd65f085c4b026b5cac48be02f523..8691dba44e2958aaf4fe00c78503361b714bca5c 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -522,6 +522,13 @@ class Isolate : public BaseIsolate {
     return AtomicOperations::LoadRelaxedIntPtr(&loading_invalidation_gen_);
   }
 
+  // Used by mutator thread to notify background compiler which fields
+  // triggered code invalidation.
+  void AddDisablingField(const Field& field);
+  // Returns Field::null() if none available in the list.
+  RawField* GetDisablingField();
+  void ClearDisablingFieldList();
+
   // Used by background compiler which field became boxed and must trigger
   // deoptimization in the mutator thread.
   void AddDeoptimizingBoxedField(const Field& field);
@@ -744,10 +751,13 @@ class Isolate : public BaseIsolate {
   intptr_t loading_invalidation_gen_;
   intptr_t top_level_parsing_count_;
 
-  // Protect access to boxed_field_list_.
-  Mutex* boxed_field_list_mutex_;
+  // Protect access to boxed_field_list_ and disabling_field_list_.
+  Mutex* field_list_mutex_;
   // List of fields that became boxed and that trigger deoptimization.
   RawGrowableObjectArray* boxed_field_list_;
+  // List of fields that were disabling code while background compiler
+  // was running.
+  RawGrowableObjectArray* disabling_field_list_;
 
   // This guards spawn_count_. An isolate cannot complete shutdown and be
   // destroyed while there are child isolates in the midst of a spawn.