Track loading happening in parallel with background compilation and abort compilation if necessary.

runtime/vm/atomic.h

Index: runtime/vm/atomic.h
diff --git a/runtime/vm/atomic.h b/runtime/vm/atomic.h
index bd489d0de36aec88030f1bc5edd88715e33db446..fc6257ec7ef95354dec1cad327cf59d7e48782ae 100644
--- a/runtime/vm/atomic.h
+++ b/runtime/vm/atomic.h
@@ -53,6 +53,12 @@ class AtomicOperations : public AllStatic {
   static uword LoadRelaxed(uword* ptr) {
     return *static_cast<volatile uword*>(ptr);
   }
+
+  // Performs a load of a word from 'ptr', but without any guarantees about
+  // memory order (i.e., no load barriers/fences).
+  static intptr_t LoadRelaxedIntPtr(intptr_t* ptr) {
+    return *static_cast<volatile intptr_t*>(ptr);
+  }
 };