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

base/memory/shared_memory_mac.cc

Index: base/memory/shared_memory_mac.cc
diff --git a/base/memory/shared_memory_mac.cc b/base/memory/shared_memory_mac.cc
index d376daa579ee0aec81ceddf0531031ff2cf376fc..2377e57f615071d16c2453646e57ed052d466c75 100644
--- a/base/memory/shared_memory_mac.cc
+++ b/base/memory/shared_memory_mac.cc
@@ -17,6 +17,7 @@
 #include "base/mac/mac_util.h"
 #include "base/mac/scoped_mach_vm.h"
 #include "base/memory/shared_memory_helper.h"
+#include "base/memory/shared_memory_tracker.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/posix/eintr_wrapper.h"
@@ -212,6 +213,7 @@ bool SharedMemory::MapAt(off_t offset, size_t bytes) {
     DCHECK_EQ(0U, reinterpret_cast<uintptr_t>(memory_) &
                       (SharedMemory::MAP_MINIMUM_ALIGNMENT - 1));
     mapped_memory_mechanism_ = shm_.type_;
+    SharedMemoryTracker::GetInstance()->IncrementMemoryUsage(*this);
   } else {
     memory_ = NULL;
   }
@@ -233,7 +235,7 @@ bool SharedMemory::Unmap() {
                          mapped_size_);
       break;
   }
-
+  SharedMemoryTracker::GetInstance()->DecrementMemoryUsage(*this);
   memory_ = NULL;
   mapped_size_ = 0;
   return true;
@@ -256,6 +258,7 @@ SharedMemoryHandle SharedMemory::TakeHandle() {
 }
 
 void SharedMemory::Close() {
+  SharedMemoryTracker::GetInstance()->DecrementMemoryUsage(*this);

[Primiano Tucci (use gerrit), 2017/01/20 16:34:52]

I think this might not be the right point.
The decription of SharedMemory::Close()  says:
// Closes the open shared memory segment. The memory will remain mapped if
// it was previously mapped.
// It is safe to call Close repeatedly.

In other words, if you Map() and then Close(), you are still using memory. Close
just frees up the file descriptor.
I believe that what you want to intercept here is the SharedMemory::Unmap()

[hajimehoshi, 2017/01/23 11:59:09]

I was wondering if the file descriptor's is still usable for ID even after
closing.

Anyway you are right that Close doesn't affect memory usage. Done.

   shm_.Close();
   shm_ = SharedMemoryHandle();
   if (shm_.type_ == SharedMemoryHandle::POSIX) {