[Tentaive patch for discussion] Add Purge+Suspend metrics as UMA.

content/child/child_discardable_shared_memory_manager.cc

Index: content/child/child_discardable_shared_memory_manager.cc
diff --git a/content/child/child_discardable_shared_memory_manager.cc b/content/child/child_discardable_shared_memory_manager.cc
index 44384491f1d4e739dadbe8a3851352bb11dc7bb0..9f44b3974f289151c0fbdcd840801d7bb58fa341 100644
--- a/content/child/child_discardable_shared_memory_manager.cc
+++ b/content/child/child_discardable_shared_memory_manager.cc
@@ -235,6 +235,13 @@ bool ChildDiscardableSharedMemoryManager::OnMemoryDump(
   return heap_.OnMemoryDump(pmd);
 }
 
+size_t ChildDiscardableSharedMemoryManager::GetMemoryUsage() const {
+  base::AutoLock lock(lock_);
+  const size_t total_size = heap_.GetSize();
+  const size_t freelist_size = heap_.GetSizeOfFreeLists();
+  return total_size - freelist_size;
+}
+
 void ChildDiscardableSharedMemoryManager::ReleaseFreeMemory() {
   base::AutoLock lock(lock_);