Initial isolate reload support

runtime/vm/become.h

Index: runtime/vm/become.h
diff --git a/runtime/vm/become.h b/runtime/vm/become.h
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+++ b/runtime/vm/become.h
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+// 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.
+
+#ifndef VM_BECOME_H_
+#define VM_BECOME_H_
+
+#include "vm/allocation.h"
+
+namespace dart {
+
+class Array;
+
+class Become : public AllStatic {
+ public:
+  // Smalltalk's one-way bulk become (Array>>#elementsForwardIdentityTo:).
+  // Redirects all pointers to elements of 'before' to the corresponding element
+  // in 'after'. Every element in 'before' is guaranteed to be dead after this

[Ivan Posva, 2016/05/16 20:58:59]

"is guaranteed to be dead" -> "is guaranteed to be not reachable"

And drop the next GC comment as it is not entirely true unless you clear the
before array before triggering the next GC. The "unreachable" comment has the
same problem though.

[Cutch, 2016/05/17 18:03:51]

Done.

+  // operation, though we won't finalize them until the next GC discovers this.
+  // Useful for atomically applying behavior and schema changes.
+  static void ElementsForwardIdentity(const Array& before, const Array& after);
+
+  // For completeness, Smalltalk also has a two-way bulk become
+  // (Array>>#elementsExchangeIdentityWith:). This is typically used in
+  // application-level virtual memory or persistence schemes, where a set of
+  // objects are swapped with so-called husks and the original objects are
+  // serialized.
+  // static void ElementsExchangeIdentity(const Array& before,

[Ivan Posva, 2016/05/16 20:58:59]

Drop this as it is not needed for reload.

[Cutch, 2016/05/17 18:03:51]

Done.

+  //                                      const Array& after);
+};
+
+}  // namespace dart
+
+#endif  // VM_BECOME_H_