Add a size estimation mechanism to StoragePartitionHttpCacheDataRemover.

net/disk_cache/blockfile/backend_impl.h

Index: net/disk_cache/blockfile/backend_impl.h
diff --git a/net/disk_cache/blockfile/backend_impl.h b/net/disk_cache/blockfile/backend_impl.h
index 3feafc1998906c6d32c6dd512d92025f6f1944fc..f8884683e8e259ac318da9d71ad54f20b69aa17b 100644
--- a/net/disk_cache/blockfile/backend_impl.h
+++ b/net/disk_cache/blockfile/backend_impl.h
@@ -73,6 +73,7 @@ class NET_EXPORT_PRIVATE BackendImpl : public Backend {
   int SyncDoomAllEntries();
   int SyncDoomEntriesBetween(base::Time initial_time,
                              base::Time end_time);
+  int SyncCalculateSizeOfAllEntries();
   int SyncDoomEntriesSince(base::Time initial_time);
   int SyncOpenNextEntry(Rankings::Iterator* iterator, Entry** next_entry);
   void SyncEndEnumeration(scoped_ptr<Rankings::Iterator> iterator);
@@ -275,6 +276,7 @@ class NET_EXPORT_PRIVATE BackendImpl : public Backend {
                          const CompletionCallback& callback) override;
   int DoomEntriesSince(base::Time initial_time,
                        const CompletionCallback& callback) override;
+  int CalculateSizeOfAllEntries(const CompletionCallback& callback) override;
   // NOTE: The blockfile Backend::Iterator::OpenNextEntry method does not modify
   // the last_used field of the entry, and therefore it does not impact the
   // eviction ranking of the entry. However, an enumeration will go through all