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

content/child/child_discardable_shared_memory_manager.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/child/child_discardable_shared_memory_manager.h"
 
 #include <inttypes.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 217 matching lines @@
                           total_size - freelist_size);
     total_dump->AddScalar("freelist_size",
                           base::trace_event::MemoryAllocatorDump::kUnitsBytes,
                           freelist_size);
     return true;
   }
 
   return heap_.OnMemoryDump(pmd);
 }
 
+size_t ChildDiscardableSharedMemoryManager::GetMemoryUsage() const {

[bashi, 2016/09/22 23:28:26]

It may be consistent when this returns a struct like malloc?

class ChildDiscardableSharedMemoryManager {
  ...
  struct Statistics {
    size_t total_size;
    size_t freelist_size;
  };
};

+  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_);
 
   size_t heap_size_prior_to_releasing_memory = heap_.GetSize();
 
   // Release both purged and free memory.
   heap_.ReleasePurgedMemory();
   heap_.ReleaseFreeMemory();
 
   if (heap_.GetSize() != heap_size_prior_to_releasing_memory)
@@ skipping 90 matching lines @@
       "discardable-memory-allocated";
   base::debug::SetCrashKeyValue(kDiscardableMemoryAllocatedKey,
                                 base::Uint64ToString(new_bytes_total));
 
   static const char kDiscardableMemoryFreeKey[] = "discardable-memory-free";
   base::debug::SetCrashKeyValue(kDiscardableMemoryFreeKey,
                                 base::Uint64ToString(new_bytes_free));
 }
 
 }  // namespace content