VM: Refactor more intrinsics of GrowableList to use IR builder.

runtime/vm/raw_object_snapshot.cc

Index: runtime/vm/raw_object_snapshot.cc
===================================================================
--- runtime/vm/raw_object_snapshot.cc	(revision 43193)
+++ runtime/vm/raw_object_snapshot.cc	(working copy)
@@ -1366,12 +1366,8 @@
 
   // Allocate context object.
   int32_t num_vars = reader->Read<int32_t>();
-  Context& context = Context::ZoneHandle(reader->isolate(), Context::null());
-  if (kind == Snapshot::kFull) {
-    context = reader->NewContext(num_vars);
-  } else {
-    context = Context::New(num_vars, HEAP_SPACE(kind));
-  }
+  Context& context = Context::ZoneHandle(
+      reader->isolate(), NEW_OBJECT_WITH_LEN(Context, num_vars));
   reader->AddBackRef(object_id, &context, kIsDeserialized);
 
   // Set the object tags.
@@ -1406,8 +1402,6 @@
   // Write out num of variables in the context.
   writer->Write<int32_t>(ptr()->num_variables_);
 
-  // Can't serialize the isolate pointer, we set it implicitly on read.
-
   // Write out all the object pointer fields.
   SnapshotWriterVisitor visitor(writer);
   visitor.VisitPointers(from(), to(ptr()->num_variables_));