Copy ICData descriptors when starting background compilation, so that they do not change while comp…

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 4b37a122bcfbeef0b0be247d830602d82f31a63d..0ed2f7cf139be45f0400da9325793a9b3c188c7f 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -1920,6 +1920,7 @@ class ICData : public Object {
                         intptr_t deopt_id,
                         intptr_t num_args_tested);
   static RawICData* NewFrom(const ICData& from, intptr_t num_args_tested);
+  static RawICData* CloneDescriptor(const ICData& from);
 
   static intptr_t TestEntryLengthFor(intptr_t num_args);
 
@@ -2616,8 +2617,13 @@ class Function : public Object {
   void SaveICDataMap(
       const ZoneGrowableArray<const ICData*>& deopt_id_to_ic_data,
       const Array& edge_counters_array) const;
+  // Uses saved ICData to populate the table 'deopt_id_to_ic_data'
   void RestoreICDataMap(
       ZoneGrowableArray<const ICData*>* deopt_id_to_ic_data) const;
+  // Copies saved ICData descriptors, so that they are invariant during
+  // background compilation.
+  void CopyICDataMap(
+      ZoneGrowableArray<const ICData*>* deopt_id_to_ic_data) const;
 
   RawArray* ic_data_array() const;
   void ClearICDataArray() const;