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..a9248605098757e8162d5da1622a9d407bc607fa 100644
--- a/content/common/discardable_shared_memory_heap.h
+++ b/content/common/discardable_shared_memory_heap.h
@@ -5,6 +5,8 @@
 #ifndef CONTENT_COMMON_DISCARDABLE_SHARED_MEMORY_HEAP_H_
 #define CONTENT_COMMON_DISCARDABLE_SHARED_MEMORY_HEAP_H_
 
+#include <vector>
+
 #include "base/callback.h"
 #include "base/containers/hash_tables.h"
 #include "base/containers/linked_list.h"
@@ -44,6 +46,25 @@ class CONTENT_EXPORT DiscardableSharedMemoryHeap {
     DISALLOW_COPY_AND_ASSIGN(Span);
   };
 
+  class CONTENT_EXPORT MemoryStatistics {

[Primiano Tucci (use gerrit), 2015/04/23 16:11:55]

do you really need CONTENT_EXPORT here?

[ssid, 2015/04/24 11:23:04]

No, removed.

+   public:
+    class SegmentStatistics {

[Primiano Tucci (use gerrit), 2015/04/23 16:11:55]

make this a struct and remove public:

[ssid, 2015/04/24 11:23:04]

Changed.

+     public:
+      size_t size;
+      size_t num_of_objects;
+      size_t used_size;
+    };
+
+    MemoryStatistics();
+    ~MemoryStatistics();
+
+    size_t block_size;
+    size_t total_size;
+    size_t total_objects;
+    size_t total_used_size;
+    std::vector<SegmentStatistics> segments_stats;
+  };
+
   explicit DiscardableSharedMemoryHeap(size_t block_size);
   ~DiscardableSharedMemoryHeap();
 
@@ -83,6 +104,9 @@ class CONTENT_EXPORT DiscardableSharedMemoryHeap {
   // Returns bytes of memory currently in the free lists.
   size_t GetSizeOfFreeLists() const;
 
+  // Fills statistics about memory used.
+  void GetMemoryStatistics(MemoryStatistics* statistics);

[reveman, 2015/04/23 17:32:30]

Why don't we just add "void DumpInto(base::trace_event::ProcessMemoryDump* pmd)"
instead of having to define and build a temporary struct+vector for this?
ChildDMM can just ask the heap instance to dump its stats...

[ssid, 2015/04/23 18:03:07]

This sounds like a good idea, since later we would have to get details about
spans, and then the api will have to change again. primiano@ WDYT?

+
  private:
   class ScopedMemorySegment {
    public:
@@ -95,6 +119,8 @@ class CONTENT_EXPORT DiscardableSharedMemoryHeap {
     bool IsUsed() const;
     bool IsResident() const;
 
+    void GetStatistics(MemoryStatistics::SegmentStatistics* segment_stats);
+
    private:
     DiscardableSharedMemoryHeap* const heap_;
     scoped_ptr<base::DiscardableSharedMemory> shared_memory_;