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

gpu/command_buffer/client/transfer_buffer.cc

Index: gpu/command_buffer/client/transfer_buffer.cc
diff --git a/gpu/command_buffer/client/transfer_buffer.cc b/gpu/command_buffer/client/transfer_buffer.cc
index 161c836c3ae87b3c88d754a045cef24f8bb2e8ee..18b15c1d93427d3f01063276c3b285c49a05f998 100644
--- a/gpu/command_buffer/client/transfer_buffer.cc
+++ b/gpu/command_buffer/client/transfer_buffer.cc
@@ -96,6 +96,14 @@ unsigned int TransferBuffer::GetFreeSize() const {
   return HaveBuffer() ? ring_buffer_->GetTotalFreeSizeNoWaiting() : 0;
 }
 
+base::SharedMemory* TransferBuffer::GetSharedMemory() const {
+  if (!HaveBuffer())
+    return nullptr;
+  if (!buffer_->backing())
+    return nullptr;
+  return buffer_->backing()->shared_memory();
+}
+
 void TransferBuffer::AllocateRingBuffer(unsigned int size) {
   for (;size >= min_buffer_size_; size /= 2) {
     int32_t id = -1;