HTMLImportLoader does not need to be ref-counted.

Since HTMLImportsController controls the lifetime of HTMLImportChild
instances, there's no need for HTMLImportLoader to be ref-counted.
We can just let it be owned by HTMLImportsController, as well.

R=morrita
BUG=

Review URL: https://codereview.chromium.org/298023007

git-svn-id: svn://svn.chromium.org/blink/trunk@174975 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[DevTools] Fix regression: console message doesn't filter by source url.

BUG=376770

Review URL: https://codereview.chromium.org/304503004

git-svn-id: svn://svn.chromium.org/blink/trunk@174976 bbb929c8-8fbe-4397-9dbb-9b2b20218538