Fix x64 GC test: ensure huge is huge enough.

runtime/vm/dart_api_impl_test.cc

 // 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.
 
 // TODO(zra): Remove when tests are ready to enable.
 #include "platform/globals.h"
 #if !defined(TARGET_ARCH_ARM64)
 
 #include "bin/builtin.h"
 #include "include/dart_api.h"
@@ skipping 2357 matching lines @@
     weak = Dart_NewWeakPersistentHandle(dead,
                                         NULL,
                                         kSmallExternalSize,
                                         NopCallback);
     EXPECT_VALID(AsHandle(weak));
     Dart_ExitScope();
   }
   EXPECT_EQ(kSmallExternalSize,
             isolate->heap()->ExternalInWords(Heap::kOld) * kWordSize);
   // Large enough to trigger GC in old space. Not actually allocated.
-  const intptr_t kHugeExternalSize = 1000 * MB;
+  const intptr_t kHugeExternalSize = Heap::kHeapSizeInMB * MB;
   Dart_NewWeakPersistentHandle(live,
                                NULL,
                                kHugeExternalSize,
                                NopCallback);
   // Expect small garbage to be collected.
   EXPECT_EQ(kHugeExternalSize,
             isolate->heap()->ExternalInWords(Heap::kOld) * kWordSize);
   Dart_DeleteWeakPersistentHandle(reinterpret_cast<Dart_Isolate>(isolate),
                                   weak);
   Dart_ExitScope();
@@ skipping 5748 matching lines @@
                                    dart_args);
   int64_t value = 0;
   result = Dart_IntegerToInt64(result, &value);
   EXPECT_VALID(result);
   EXPECT_EQ(6, value);
 }
 
 }  // namespace dart
 
 #endif  // !defined(TARGET_ARCH_ARM64)