Don't allocate on the Dart heap during Bigint::ToCString().

runtime/vm/object.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_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 6619 matching lines @@
   // Accessors used by native calls from Dart.
   RawBool* neg() const { return raw_ptr()->neg_; }
   RawSmi* used() const { return raw_ptr()->used_; }
   RawTypedData* digits() const { return raw_ptr()->digits_; }
 
   // Accessors used by runtime calls from C++.
   bool Neg() const;
   intptr_t Used() const;
   uint32_t DigitAt(intptr_t index) const;
 
-  const char* ToDecCString(uword (*allocator)(intptr_t size)) const;
-  const char* ToHexCString(uword (*allocator)(intptr_t size)) const;
+  const char* ToDecCString(Zone* zone) const;
+  const char* ToHexCString(Zone* zone) const;
 
   static const intptr_t kBitsPerDigit = 32;  // Same as _Bigint._DIGIT_BITS
   static const intptr_t kBytesPerDigit = 4;
   static const int64_t kDigitBase = 1LL << kBitsPerDigit;
   static const int64_t kDigitMask = kDigitBase - 1;
 
   static RawBigint* New(Heap::Space space = Heap::kNew);  // For snapshots.
 
   static RawBigint* New(bool neg, intptr_t used, const TypedData& digits,
                         Heap::Space space = Heap::kNew);
@@ skipping 2359 matching lines @@
 
 inline void TypeArguments::SetHash(intptr_t value) const {
   // This is only safe because we create a new Smi, which does not cause
   // heap allocation.
   StoreSmi(&raw_ptr()->hash_, Smi::New(value));
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_