[vm, gc] Require a safepoint for heap iteration.

runtime/vm/clustered_snapshot.cc

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/clustered_snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart.h"
@@ skipping 5331 matching lines @@
   // generated from a VM that has loaded this snapshots, much like app-jit
   // snapshots.
   if ((vm_snapshot_data_buffer != NULL) && (kind != Snapshot::kFullAOT)) {
     NOT_IN_PRODUCT(TimelineDurationScope tds(
         thread(), Timeline::GetIsolateStream(), "PrepareNewVMIsolate"));
 
     // Collect all the token stream objects into an array so that we can write
     // it out as part of the VM isolate snapshot. We first count the number of
     // token streams, allocate an array and then fill it up with the token
     // streams.
-    SnapshotTokenStreamVisitor token_streams_counter(thread());
-    heap()->IterateOldObjects(&token_streams_counter);
-    Dart::vm_isolate()->heap()->IterateOldObjects(&token_streams_counter);
-    intptr_t count = token_streams_counter.count();
-    token_streams_ = Array::New(count, Heap::kOld);
-    SnapshotTokenStreamVisitor script_visitor(thread(), &token_streams_);
-    heap()->IterateOldObjects(&script_visitor);
-    Dart::vm_isolate()->heap()->IterateOldObjects(&script_visitor);
-    ASSERT(script_visitor.count() == count);
+    {
+      HeapIterationScope iteration(thread());
+      SnapshotTokenStreamVisitor token_streams_counter(thread());
+      iteration.IterateObjects(&token_streams_counter);
+      iteration.IterateVMIsolateObjects(&token_streams_counter);
+      intptr_t count = token_streams_counter.count();
+      token_streams_ = Array::New(count, Heap::kOld);
+      SnapshotTokenStreamVisitor script_visitor(thread(), &token_streams_);
+      iteration.IterateObjects(&script_visitor);
+      iteration.IterateVMIsolateObjects(&script_visitor);
+      ASSERT(script_visitor.count() == count);
+    }
 
     // Tuck away the current symbol table.
     saved_symbol_table_ = object_store->symbol_table();
 
     // Create a unified symbol table that will be written as the vm isolate's
     // symbol table.
     new_vm_symbol_table_ = Symbols::UnifiedSymbolTable();
 
     // Create an empty symbol table that will be written as the isolate's symbol
     // table.
@@ skipping 160 matching lines @@
     thread_->isolate()->SetupImagePage(data_buffer_,
                                        /* is_executable */ false);
   }
 
   deserializer.ReadIsolateSnapshot(thread_->isolate()->object_store());
 
   return ApiError::null();
 }
 
 }  // namespace dart