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

gpu/command_buffer/common/buffer.cc

Index: gpu/command_buffer/common/buffer.cc
diff --git a/gpu/command_buffer/common/buffer.cc b/gpu/command_buffer/common/buffer.cc
index 13b606c3286734c4ad04723fd5248239b27143f1..7aa13f3f3080f9226d13813ceba9316445174cd5 100644
--- a/gpu/command_buffer/common/buffer.cc
+++ b/gpu/command_buffer/common/buffer.cc
@@ -14,8 +14,8 @@
 
 namespace gpu {
 
-bool BufferBacking::is_shared() const {
-  return false;
+base::SharedMemory* BufferBacking::shared_memory() {
+  return nullptr;
 }
 
 SharedMemoryBufferBacking::SharedMemoryBufferBacking(
@@ -25,8 +25,8 @@ SharedMemoryBufferBacking::SharedMemoryBufferBacking(
 
 SharedMemoryBufferBacking::~SharedMemoryBufferBacking() {}
 
-bool SharedMemoryBufferBacking::is_shared() const {
-  return true;
+base::SharedMemory* SharedMemoryBufferBacking::shared_memory() {
+  return shared_memory_.get();
 }
 
 void* SharedMemoryBufferBacking::GetMemory() const {