Revert "[vm] Revise Dart_IntegerToHexCString to avoid dependency on Bigint"

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 "lib/stacktrace.h"
 #include "platform/assert.h"
@@ skipping 2171 matching lines @@
 
 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();
-  *value = int_obj.ToHexCString(scope_zone);
+  if (int_obj.IsSmi() || int_obj.IsMint()) {
+    const Bigint& bigint =
+        Bigint::Handle(Z, Bigint::NewFromInt64(int_obj.AsInt64Value()));
+    *value = bigint.ToHexCString(scope_zone);
+  } else {
+    *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));
 }
 
 DART_EXPORT Dart_Handle Dart_DoubleValue(Dart_Handle double_obj,
@@ skipping 4536 matching lines @@
 #endif
 }
 
 DART_EXPORT void Dart_DumpNativeStackTrace(void* context) {
 #ifndef PRODUCT
   Profiler::DumpStackTrace(context);
 #endif
 }
 
 }  // namespace dart