Rename references to "external pages" as "snapshot pages" to avoid confusion with the kind of exter…

runtime/vm/benchmark_test.cc

Index: runtime/vm/benchmark_test.cc
diff --git a/runtime/vm/benchmark_test.cc b/runtime/vm/benchmark_test.cc
index 4b34e20abcbb564c5b5f1a1b890bbe99bf0e245f..83cd23f7c1472f25befcc82b312901757f82ebfb 100644
--- a/runtime/vm/benchmark_test.cc
+++ b/runtime/vm/benchmark_test.cc
@@ -521,7 +521,7 @@ BENCHMARK_SIZE(CoreSnapshotSize) {
   // Write snapshot with object content.
   FullSnapshotWriter writer(Snapshot::kCore, &vm_snapshot_data_buffer,
                             &isolate_snapshot_data_buffer, &malloc_allocator,
-                            NULL, NULL /* instructions_writer */);
+                            NULL, NULL /* image_writer */);
   writer.WriteFullSnapshot();
   const Snapshot* snapshot =
       Snapshot::SetupFromBuffer(isolate_snapshot_data_buffer);
@@ -559,7 +559,7 @@ BENCHMARK_SIZE(StandaloneSnapshotSize) {
   // Write snapshot with object content.
   FullSnapshotWriter writer(Snapshot::kCore, &vm_snapshot_data_buffer,
                             &isolate_snapshot_data_buffer, &malloc_allocator,
-                            NULL, NULL /* instructions_writer */);
+                            NULL, NULL /* image_writer */);
   writer.WriteFullSnapshot();
   const Snapshot* snapshot =
       Snapshot::SetupFromBuffer(isolate_snapshot_data_buffer);