Add a size estimation mechanism to StoragePartitionHttpCacheDataRemover.

net/disk_cache/memory/mem_backend_impl.h

Index: net/disk_cache/memory/mem_backend_impl.h
diff --git a/net/disk_cache/memory/mem_backend_impl.h b/net/disk_cache/memory/mem_backend_impl.h
index 6be8e946797326ed0e3ed1e4ba20791382eefccf..d3bb0058723f56e81937172dcf8f26956528dbb9 100644
--- a/net/disk_cache/memory/mem_backend_impl.h
+++ b/net/disk_cache/memory/mem_backend_impl.h
@@ -80,6 +80,7 @@ class NET_EXPORT_PRIVATE MemBackendImpl : public Backend {
                          const CompletionCallback& callback) override;
   int DoomEntriesSince(base::Time initial_time,
                        const CompletionCallback& callback) override;
+  int CalculateSizeOfAllEntries(const CompletionCallback& callback) override;
   scoped_ptr<Iterator> CreateIterator() override;
   void GetStats(base::StringPairs* stats) override {}
   void OnExternalCacheHit(const std::string& key) override;