[tracing] Display the locked size of discardable memory segment.

content/common/discardable_shared_memory_heap.cc

Index: content/common/discardable_shared_memory_heap.cc
diff --git a/content/common/discardable_shared_memory_heap.cc b/content/common/discardable_shared_memory_heap.cc
index ccf2729c557f660e3b675def1393449be60564dd..ea614b40d326083d246d1772dbc40fd1807f4323 100644
--- a/content/common/discardable_shared_memory_heap.cc
+++ b/content/common/discardable_shared_memory_heap.cc
@@ -396,6 +396,18 @@ void DiscardableSharedMemoryHeap::OnMemoryDump(
                       base::trace_event::MemoryAllocatorDump::kUnitsBytes,
                       static_cast<uint64_t>(allocated_objects_size_in_bytes));
 
+  // Total size of discardable memory segments locked by the clients.
+  const size_t locked_size = shared_memory->LockedSize();
+  obj_dump->AddScalar("client_locked_size",

[reveman, 2015/09/29 12:29:10]

I think it will be enough to dump the exact locked size. What's actually locked
depends on the OS and the browser process should be responsible for dumping
that.

[ssid, 2015/09/29 16:03:55]

Sounds good.

+                      base::trace_event::MemoryAllocatorDump::kUnitsBytes,
+                      locked_size);
+
+  // Size of the discardable segment actually locked by the platform
+  // independent lock.
+  obj_dump->AddScalar("actual_locked_size",
+                      base::trace_event::MemoryAllocatorDump::kUnitsBytes,
+                      locked_size ? size : 0u);
+
   // Emit an ownership edge towards a global allocator dump node. This allows
   // to avoid double-counting segments when both browser and child process emit
   // them. In the special case of single-process-mode, this will be the only