content: Remove non-thread-safe use of WeakPtrs.

content/child/child_thread_impl.cc

 // Copyright (c) 2012 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.
 
 #include "content/child/child_thread_impl.h"
 
 #include <signal.h>
 
 #include <string>
 
@@ skipping 459 matching lines @@
       new ChildSharedBitmapManager(thread_safe_sender()));
 
   gpu_memory_buffer_manager_.reset(
       new ChildGpuMemoryBufferManager(thread_safe_sender()));
 
   discardable_shared_memory_manager_.reset(
       new ChildDiscardableSharedMemoryManager(thread_safe_sender()));
 }
 
 ChildThreadImpl::~ChildThreadImpl() {
+  // ChildDiscardableSharedMemoryManager has to be destroyed while
+  // |thread_safe_sender_| is still valid.
+  discardable_shared_memory_manager_.reset();
+
 #if defined(OS_ANDROID)
   {
     base::AutoLock lock(g_lazy_child_thread_lock.Get());
     g_child_thread = nullptr;
   }
 #endif
 
 #ifdef IPC_MESSAGE_LOG_ENABLED
   IPC::Logging::GetInstance()->SetIPCSender(NULL);
 #endif
@@ skipping 255 matching lines @@
   // doesn't cause such issues. TODO(gab): Remove this once the experiment is
   // over (http://crbug.com/458594).
   base::FieldTrial* trial =
       base::FieldTrialList::Find("BackgroundRendererProcesses");
   if (trial && trial->group_name() == "AllowBackgroundModeFromRenderer")
     base::Process::Current().SetProcessBackgrounded(background);
 #endif  // OS_WIN
 }
 
 }  // namespace content