Reintroducing MallocHooks changes with fix for hooks being called when in execvpe after a fork whil…

runtime/vm/malloc_hooks_unsupported.cc

 // Copyright (c) 2017, 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.
 
-#if defined(DART_USE_TCMALLOC)
+#include "platform/globals.h"
+
+#if !defined(DART_USE_TCMALLOC) || defined(PRODUCT)
 
 #include "vm/malloc_hooks.h"
 
 namespace dart {
 
-void MallocHooks::Init() {
-  // TODO(bkonyi): Implement
+void MallocHooks::InitOnce() {
+  // Do nothing.
+}
+
+
+void MallocHooks::TearDown() {
+  // Do nothing.
+}
+
+
+void MallocHooks::ResetStats() {
+  // Do nothing.
+}
+
+
+intptr_t MallocHooks::allocation_count() {
+  return 0;
+}
+
+
+intptr_t MallocHooks::heap_allocated_memory_in_bytes() {
+  return 0;
 }
 
 }  // namespace dart
 
-#endif  // defined(DART_USE_TCMALLOC)
+#endif  // defined(DART_USE_TCMALLOC) || defined(PRODUCT)