[VM interpreter] Use write barrier in implicit setter.

Change-Id: I68351f5e009c1101bd7afc443b1b016197f62032
Reviewed-on: https://dart-review.googlesource.com/68427
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Régis Crelier <[email protected]>

Author: crelier

runtime/vm/interpreter.cc

@@ -1038,7 +1038,9 @@ DART_NOINLINE bool Interpreter::ProcessInvocation(bool* invoked,
           }
         }
       }
-      reinterpret_cast<RawObject**>(instance->ptr())[offset_in_words] = value;
+      instance->StorePointer(
+          reinterpret_cast<RawObject**>(instance->ptr()) + offset_in_words,
+          value);
       *SP = call_base;
       **SP = null_value;
       *invoked = true;