Added page to Observatory to display native memory allocation information.

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/allocation.h"
 #include "vm/globals.h"
 
 namespace dart {
 
 class JSONObject;
 class Sample;
 
 class MallocHooks : public AllStatic {
  public:
   static void InitOnce();
   static void TearDown();
   static bool ProfilingEnabled();
   static bool stack_trace_collection_enabled();
   static void set_stack_trace_collection_enabled(bool enabled);
   static void ResetStats();
   static bool Active();
   static void PrintToJSONObject(JSONObject* jsobj);
   static Sample* GetSample(const void* ptr);
-
+  static bool NativeAllocationFreed(const void* ptr);
   static intptr_t allocation_count();
   static intptr_t heap_allocated_memory_in_bytes();
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_MALLOC_HOOKS_H_