Add a size estimation mechanism to StoragePartitionHttpCacheDataRemover.

net/disk_cache/memory/mem_backend_impl.cc

Index: net/disk_cache/memory/mem_backend_impl.cc
diff --git a/net/disk_cache/memory/mem_backend_impl.cc b/net/disk_cache/memory/mem_backend_impl.cc
index 8350963c6e39be56570143a28b24f25251935e9c..ca8cf1b7d6b23291f3c79743755d0c57456cf451 100644
--- a/net/disk_cache/memory/mem_backend_impl.cc
+++ b/net/disk_cache/memory/mem_backend_impl.cc
@@ -182,6 +182,12 @@ int MemBackendImpl::DoomEntriesSince(const base::Time initial_time,
   return net::ERR_FAILED;
 }
 
+int MemBackendImpl::CalculateSizeOfAllEntries(
+    const CompletionCallback& callback) {
+  // TODO(msramek): Implement.
+  return net::ERR_NOT_IMPLEMENTED;
+}
+
 class MemBackendImpl::MemIterator : public Backend::Iterator {
  public:
   explicit MemIterator(base::WeakPtr<MemBackendImpl> backend)