[WIP] Add SharedMemoryTracker to dump base::SharedMemory usage

components/discardable_memory/service/discardable_shared_memory_manager.cc

 // Copyright 2014 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 "components/discardable_memory/service/discardable_shared_memory_manager.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/atomic_sequence_num.h"
@@ skipping 312 matching lines @@
       // double-count them in tracing. If, instead, no other process will emit a
       // dump with the same guid, the segment will be accounted to the browser.
       const uint64_t client_tracing_id =
           ClientProcessUniqueIdToTracingProcessId(client_id);
       base::trace_event::MemoryAllocatorDumpGuid shared_segment_guid =
           DiscardableSharedMemoryHeap::GetSegmentGUIDForTracing(
               client_tracing_id, segment_id);
       pmd->CreateSharedGlobalAllocatorDump(shared_segment_guid);
       pmd->AddOwnershipEdge(dump->guid(), shared_segment_guid);
 
+// TODO(hajimehoshi): base::SharedMemoryTracker::AddOwnershipEdges should
+// be used instead of CreateSharedGlobalAllocatorDump, but the |dump|
+// doesn't have 'size' attribute here and it wouldn't make sense so far.
+
 #if defined(COUNT_RESIDENT_BYTES_SUPPORTED)
       if (args.level_of_detail ==
           base::trace_event::MemoryDumpLevelOfDetail::DETAILED) {
         size_t resident_size =
             base::trace_event::ProcessMemoryDump::CountResidentBytes(
                 segment->memory()->memory(), segment->memory()->mapped_size());
 
         // This is added to the global dump since it has to be attributed to
         // both the allocator dumps involved.
         pmd->GetSharedGlobalAllocatorDump(shared_segment_guid)
@@ skipping 283 matching lines @@
     return;
 
   enforce_memory_policy_pending_ = true;
   DCHECK(enforce_memory_policy_task_runner_);
   enforce_memory_policy_task_runner_->PostDelayedTask(
       FROM_HERE, enforce_memory_policy_callback_,
       base::TimeDelta::FromMilliseconds(kEnforceMemoryPolicyDelayMs));
 }
 
 }  // namespace discardable_memory