When deduplicating program metadata, try to use objects from the VM isolate.

runtime/vm/snapshot.h

 // Copyright (c) 2012, 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 RUNTIME_VM_SNAPSHOT_H_
 #define RUNTIME_VM_SNAPSHOT_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/bitfield.h"
@@ skipping 308 matching lines @@
 
  private:
   Object* reference_;
   DeserializeState state_;
   bool defer_canonicalization_;
   ZoneGrowableArray<intptr_t>* patch_records_;
 };
 
 class ImageReader : public ZoneAllocated {
  public:
-  ImageReader(const uint8_t* instructions_buffer, const uint8_t* data_buffer)
-      : instructions_buffer_(instructions_buffer), data_buffer_(data_buffer) {
-    ASSERT(instructions_buffer != NULL);
-    ASSERT(data_buffer != NULL);
-    ASSERT(Utils::IsAligned(reinterpret_cast<uword>(instructions_buffer),
-                            OS::PreferredCodeAlignment()));
-  }
+  ImageReader(const uint8_t* instructions_buffer, const uint8_t* data_buffer);
 
   RawInstructions* GetInstructionsAt(int32_t offset);
   RawObject* GetObjectAt(int32_t offset);
 
  private:
   const uint8_t* instructions_buffer_;
   const uint8_t* data_buffer_;
+  const uint8_t* vm_instructions_buffer_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageReader);
 };
 
 // Reads a snapshot into objects.
 class SnapshotReader : public BaseReader {
  public:
   Thread* thread() const { return thread_; }
   Zone* zone() const { return zone_; }
   Isolate* isolate() const { return thread_->isolate(); }
@@ skipping 639 matching lines @@
  private:
   SnapshotWriter* writer_;
   bool as_references_;
 
   DISALLOW_COPY_AND_ASSIGN(SnapshotWriterVisitor);
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_SNAPSHOT_H_