Keep zone cached in SnapshotReader to allow removing ZoneHandle(Isolate*) interface.

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 VM_SNAPSHOT_H_
 #define VM_SNAPSHOT_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/bitfield.h"
@@ skipping 227 matching lines @@
   ReadStream stream_;  // input stream.
 };
 
 
 // Reads a snapshot into objects.
 class SnapshotReader : public BaseReader {
  public:
   SnapshotReader(const uint8_t* buffer,
                  intptr_t size,
                  Snapshot::Kind kind,
-                 Isolate* isolate);
+                 Isolate* isolate,
+                 Zone* zone);
   ~SnapshotReader() { }
 
+  Zone* zone() const { return zone_; }
   Isolate* isolate() const { return isolate_; }
   Heap* heap() const { return heap_; }
   ObjectStore* object_store() const { return isolate_->object_store(); }
   ClassTable* class_table() const { return isolate_->class_table(); }
   PassiveObject* PassiveObjectHandle() { return &pobj_; }
   Array* ArrayHandle() { return &array_; }
   String* StringHandle() { return &str_; }
   AbstractType* TypeHandle() { return &type_; }
   TypeArguments* TypeArgumentsHandle() { return &type_arguments_; }
   Array* TokensHandle() { return &tokens_; }
@@ skipping 105 matching lines @@
   intptr_t LookupInternalClass(intptr_t class_header);
 
   void ArrayReadFrom(const Array& result, intptr_t len, intptr_t tags);
 
   intptr_t NextAvailableObjectId() const;
 
   void SetReadException(const char* msg);
 
   Snapshot::Kind kind_;  // Indicates type of snapshot(full, script, message).
   Isolate* isolate_;  // Current isolate.
+  Zone* zone_;  // Zone for allocations while reading snapshot.
   Heap* heap_;  // Heap of the current isolate.
   PageSpace* old_space_;  // Old space of the current isolate.
   Class& cls_;  // Temporary Class handle.
   Object& obj_;  // Temporary Object handle.
   PassiveObject& pobj_;  // Temporary PassiveObject handle.
   Array& array_;  // Temporary Array handle.
   Field& field_;  // Temporary Field handle.
   String& str_;  // Temporary String handle.
   Library& library_;  // Temporary library handle.
   AbstractType& type_;  // Temporary type handle.
@@ skipping 361 matching lines @@
  private:
   SnapshotWriter* writer_;
   bool as_references_;
 
   DISALLOW_COPY_AND_ASSIGN(SnapshotWriterVisitor);
 };
 
 }  // namespace dart
 
 #endif  // VM_SNAPSHOT_H_