Adding discardable memory dump provider.

content/common/discardable_shared_memory_heap.h

Index: content/common/discardable_shared_memory_heap.h
diff --git a/content/common/discardable_shared_memory_heap.h b/content/common/discardable_shared_memory_heap.h
index 23b9cfb87d237dc1a4016dc029a0086aaf05fca1..21607dd3532437490050c7a48032854fe2b94f58 100644
--- a/content/common/discardable_shared_memory_heap.h
+++ b/content/common/discardable_shared_memory_heap.h
@@ -10,6 +10,7 @@
 #include "base/containers/linked_list.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/scoped_vector.h"
+#include "base/trace_event/process_memory_dump.h"
 #include "content/common/content_export.h"
 
 namespace base {
@@ -83,6 +84,9 @@ class CONTENT_EXPORT DiscardableSharedMemoryHeap {
   // Returns bytes of memory currently in the free lists.
   size_t GetSizeOfFreeLists() const;
 
+  // Dumps memory statistics for chrome://tracing.
+  bool DumpMemoryStatisticsInto(base::trace_event::ProcessMemoryDump* pmd);
+
  private:
   class ScopedMemorySegment {
    public:
@@ -96,6 +100,8 @@ class CONTENT_EXPORT DiscardableSharedMemoryHeap {
     bool IsResident() const;
 
    private:
+    friend class DiscardableSharedMemoryHeap;

[reveman, 2015/04/24 14:19:36]

hm, sorry I missed this in my previous review. What do you think about removing
this friend class and instead add a public DumpInto() function that just calls
heap_->DumpMemoryInto(shared_memory_.get(), size_, id_)? It's not ideal to have
this type of indirection but that's what we have for IsUsed, IsResident so I
think it would be the most consistent way to implement this right now.

[ssid, 2015/04/27 11:19:21]

Yes, I tried to explain this indirection in last patch, I wasn't clear. made
changes now.

+
     DiscardableSharedMemoryHeap* const heap_;
     scoped_ptr<base::DiscardableSharedMemory> shared_memory_;
     const size_t size_;

[reveman, 2015/04/24 14:19:36]

I think we should add "const DiscardableSharedMemoryId id_;" here and use that
as segment id. This id is unique and won't change between dumps like the vector
index.

[ssid, 2015/04/27 11:19:21]

Done.