Indexed DB: Restore content-type to deserialized Blobs

The Blob type was serialized/restored correctly on the Blink side, but
not on the Chromium side, so when reading a Blob as a stream the
type would be unset.

BUG=408120
R=cmumford@chromium.org
TEST=https://codereview.chromium.org/509213005

Review URL: https://codereview.chromium.org/511373002

Cr-Commit-Position: refs/heads/master@{#292485}

content/browser/indexed_db/indexed_db_callbacks.cc

@@ -246,6 +246,7 @@ static std::string CreateBlobData(
 
   uuid = base::GenerateGUID();
   scoped_refptr<storage::BlobData> blob_data = new storage::BlobData(uuid);
+  blob_data->set_content_type(base::UTF16ToUTF8(blob_info.type()));
   blob_data->AppendFile(
       blob_info.file_path(), 0, blob_info.size(), blob_info.last_modified());
   scoped_ptr<storage::BlobDataHandle> blob_data_handle(