Reland &quotCorrectly set ScriptState in the image loader microtask&quot

      Original review: https://codereview.chromium.org/1153233002/

BUG=487155
R=haraken@chromium.org

Review URL: https://codereview.chromium.org/1163543002

git-svn-id: svn://svn.chromium.org/blink/trunk@196071 bbb929c8-8fbe-4397-9dbb-9b2b20218538