message: Fix leak in srcset test: add call to Detach()
diff: @@ -172,6 +172,7 @@ TEST_F(SrcSetSlotTest, BasicOperation) {
  EXPECT_EQ("<img srcset=\"a.jpg, b.pagespeed.webp 100w, c.png 1000w\"/>",
  GetHtmlDomAsString());
  + collection->Detach();
  }
  } // namespace net_instaweb
  