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

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, 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 "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "lib/stacktrace.h"
@@ skipping 2284 matching lines @@
     if (bigint.FitsIntoUint64()) {
       *value = bigint.AsUint64Value();
       return Api::Success();
     }
   }
   return Api::NewError("%s: Integer %s cannot be represented as a uint64_t.",
                        CURRENT_FUNC, int_obj.ToCString());
 }
 
 
-static uword BigintAllocate(intptr_t size) {
-  return Api::TopScope(Thread::Current())->zone()->AllocUnsafe(size);
-}
-
-
 DART_EXPORT Dart_Handle Dart_IntegerToHexCString(Dart_Handle integer,
                                                  const char** value) {
   API_TIMELINE_DURATION;
   DARTSCOPE(Thread::Current());
   const Integer& int_obj = Api::UnwrapIntegerHandle(Z, integer);
   if (int_obj.IsNull()) {
     RETURN_TYPE_ERROR(Z, integer, Integer);
   }
+  Zone* scope_zone = Api::TopScope(Thread::Current())->zone();
   if (int_obj.IsSmi() || int_obj.IsMint()) {
     const Bigint& bigint = Bigint::Handle(Z,
         Bigint::NewFromInt64(int_obj.AsInt64Value()));
-    *value = bigint.ToHexCString(BigintAllocate);
+    *value = bigint.ToHexCString(scope_zone);
   } else {
-    *value = Bigint::Cast(int_obj).ToHexCString(BigintAllocate);
+    *value = Bigint::Cast(int_obj).ToHexCString(scope_zone);
   }
   return Api::Success();
 }
 
 
 DART_EXPORT Dart_Handle Dart_NewDouble(double value) {
   DARTSCOPE(Thread::Current());
   CHECK_CALLBACK_STATE(T);
   return Api::NewHandle(T, Double::New(value));
 }
@@ skipping 4310 matching lines @@
 
 DART_EXPORT bool Dart_IsPrecompiledRuntime() {
 #if defined(DART_PRECOMPILED_RUNTIME)
   return true;
 #else
   return false;
 #endif
 }
 
 }  // namespace dart