[tracing] directly use memory-infra from blink -> base

base/trace_event/memory_dump_provider.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_TRACE_EVENT_MEMORY_DUMP_PROVIDER_H_
 #define BASE_TRACE_EVENT_MEMORY_DUMP_PROVIDER_H_
 
 #include "base/base_export.h"
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/trace_event/memory_dump_request_args.h"
 
 namespace base {
+
+class SingleThreadTaskRunner;
+
 namespace trace_event {
 
 class ProcessMemoryDump;
 
 // Args passed to OnMemoryDump(). This is to avoid rewriting all the subclasses
 // in the codebase when extending the MemoryDumpProvider API.
 struct MemoryDumpArgs {
   MemoryDumpLevelOfDetail level_of_detail;
 };
 
 // The contract interface that memory dump providers must implement.
 class BASE_EXPORT MemoryDumpProvider {
  public:
+  // Helper methods to register/unregister a memory dump provider.
+  // The MemoryDumpManager does NOT take memory ownership of |dump_provider|,
+  // which is expected to either be a singleton or unregister itself.
+  // If the optional |task_runner| argument is non-null, all the calls to the
+  // |dump_provider| will be issued on the given thread. Otherwise, the |mdp|
+  // should be able to handle calls on arbitrary threads.
+  static void Register(

[Ruud van Asseldonk, 2015/10/08 18:40:54]

Does this introduce two ways of doing the same thing,
|MemoryDumpProvider::Register(mdp)| vs
|MemoryDumpManager::GetInstance()->RegisterDumpProvider(mdp)|? Why is that
required?

+      MemoryDumpProvider* dump_provider,
+      const scoped_refptr<SingleThreadTaskRunner>& task_runner);
+
+  // Similar to Register, but all the calls are guaranteed to happen on the
+  // current thread's task runner.
+  static void RegisterOnCurrentThread(MemoryDumpProvider* dump_provider);
+
+  static void Unregister(MemoryDumpProvider* dump_provider);
+
   // Called by the MemoryDumpManager when generating memory dumps.
   // The |args| specify if the embedder should generate light/heavy dumps on
   // dump requests. The embedder should return true if the |pmd| was
   // successfully populated, false if something went wrong and the dump should
   // be considered invalid.
   // (Note, the MemoryDumpManager has a fail-safe logic which will disable the
   // MemoryDumpProvider for the entire trace session if it fails consistently).
   virtual bool OnMemoryDump(const MemoryDumpArgs& args,
                             ProcessMemoryDump* pmd) = 0;
 
  protected:
   MemoryDumpProvider() {}
   virtual ~MemoryDumpProvider() {}
 
   DISALLOW_COPY_AND_ASSIGN(MemoryDumpProvider);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_MEMORY_DUMP_PROVIDER_H_