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

cc/tiles/gpu_image_decode_cache.cc

 // Copyright 2016 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 "cc/tiles/gpu_image_decode_cache.h"
 
 #include <inttypes.h>
 
 #include "base/debug/alias.h"
 #include "base/memory/discardable_memory_allocator.h"
@@ skipping 601 matching lines @@
                          ->fID;
       MemoryAllocatorDumpGuid guid = gl::GetGLTextureClientGUIDForTracing(
           context_->ContextSupport()->ShareGroupTracingGUID(), gl_id);
 
       // kImportance is somewhat arbitrary - we chose 3 to be higher than the
       // value used in the GPU process (1), and Skia (2), causing us to appear
       // as the owner in memory traces.
       const int kImportance = 3;
       pmd->CreateSharedGlobalAllocatorDump(guid);
       pmd->AddOwnershipEdge(dump->guid(), guid, kImportance);
+      // TODO(hajimehoshi): |image_data::data_| might be allocated in
+      // DiscardableSharedMemory. Get shared memory handle of that and call
+      // base::SharedMemoryDumpProvider::AddOwnershipEdgeToSharedGlobalDump here
     }
   }
 
   return true;
 }
 
 void GpuImageDecodeCache::DecodeImage(const DrawImage& draw_image) {
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "GpuImageDecodeCache::DecodeImage");
   base::AutoLock lock(lock_);
@@ skipping 599 matching lines @@
       EnsureCapacity(0);
       break;
     }
     case base::MemoryState::UNKNOWN:
       // NOT_REACHED.
       break;
   }
 }
 
 }  // namespace cc