Reintroducing MallocHooks changes with fix for infinite loop in MallocHooks on Platform::Exit.

runtime/vm/malloc_hooks.h

 // 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.
 
 #ifndef RUNTIME_VM_MALLOC_HOOKS_H_
 #define RUNTIME_VM_MALLOC_HOOKS_H_
 
 #include "vm/globals.h"
 
 namespace dart {
 
 class MallocHooks {
-  static void Init();
+ public:
+  static void InitOnce();
+  static void TearDown();
+  static void ResetStats();
+
+  static intptr_t allocation_count();
+  static intptr_t heap_allocated_memory_in_bytes();
 
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(MallocHooks);
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_MALLOC_HOOKS_H_