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

gpu/ipc/service/gpu_command_buffer_stub.cc

Index: gpu/ipc/service/gpu_command_buffer_stub.cc
diff --git a/gpu/ipc/service/gpu_command_buffer_stub.cc b/gpu/ipc/service/gpu_command_buffer_stub.cc
index a798308542982dba5e16372a4b5adece6dec6725..6ae5fa7b718ed268f13d33ce7b8e7cb72ed2d028 100644
--- a/gpu/ipc/service/gpu_command_buffer_stub.cc
+++ b/gpu/ipc/service/gpu_command_buffer_stub.cc
@@ -829,6 +829,8 @@ bool GpuCommandBufferStub::Initialize(
     DLOG(ERROR) << "Failed to map shared state buffer.";
     return false;
   }
+  const int kImportance = 2;
+  shared_state_shm->set_importance(kImportance);
   command_buffer_->SetSharedStateBuffer(MakeBackingFromSharedMemory(
       std::move(shared_state_shm), kSharedStateSize));
 
@@ -1013,7 +1015,8 @@ void GpuCommandBufferStub::OnRegisterTransferBuffer(
     DVLOG(0) << "Failed to map shared memory.";
     return;
   }
-
+  const int kImportance = 2;
+  shared_memory->set_importance(kImportance);
   if (command_buffer_) {
     command_buffer_->RegisterTransferBuffer(
         id, MakeBackingFromSharedMemory(std::move(shared_memory), size));