[tracing] Add memory statistics from level db clients to tracing.

content/browser/dom_storage/session_storage_database.h

Index: content/browser/dom_storage/session_storage_database.h
diff --git a/content/browser/dom_storage/session_storage_database.h b/content/browser/dom_storage/session_storage_database.h
index 4260e4adb567600c6c8a42c47e41b802d876bd2f..0d8f00880b085a57c95234873859deffdedf4659 100644
--- a/content/browser/dom_storage/session_storage_database.h
+++ b/content/browser/dom_storage/session_storage_database.h
@@ -12,6 +12,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/synchronization/lock.h"
+#include "base/trace_event/memory_dump_provider.h"
 #include "content/common/content_export.h"
 #include "content/common/dom_storage/dom_storage_types.h"
 #include "third_party/leveldatabase/src/include/leveldb/status.h"
@@ -33,8 +34,9 @@ namespace content {
 // Only one thread is allowed to call the public functions other than
 // ReadAreaValues and ReadNamespacesAndOrigins. Other threads are allowed to
 // call ReadAreaValues and ReadNamespacesAndOrigins.
-class CONTENT_EXPORT SessionStorageDatabase :
-    public base::RefCountedThreadSafe<SessionStorageDatabase> {
+class CONTENT_EXPORT SessionStorageDatabase
+    : public base::RefCountedThreadSafe<SessionStorageDatabase>,
+      public base::trace_event::MemoryDumpProvider {
  public:
   explicit SessionStorageDatabase(const base::FilePath& file_path);
 
@@ -72,13 +74,17 @@ class CONTENT_EXPORT SessionStorageDatabase :
   bool ReadNamespacesAndOrigins(
       std::map<std::string, std::vector<GURL> >* namespaces_and_origins);
 
+  // base::trace_event::MemoryDumpProvider implementation.
+  bool OnMemoryDump(const base::trace_event::MemoryDumpArgs& args,
+                    base::trace_event::ProcessMemoryDump* pmd) override;
+
  private:
   friend class base::RefCountedThreadSafe<SessionStorageDatabase>;
   class DBOperation;
   friend class SessionStorageDatabase::DBOperation;
   friend class SessionStorageDatabaseTest;
 
-  ~SessionStorageDatabase();
+  ~SessionStorageDatabase() override;
 
   // Opens the database at file_path_ if it exists already and creates it if
   // |create_if_needed| is true. Returns true if the database was opened, false