Fixed image-sizes-js-change flakiness

Switched from using dumpResourceRequestCallbacks to using direct
memoryCache APIs in internals.

BUG=426041

Review URL: https://codereview.chromium.org/675853003

git-svn-id: svn://svn.chromium.org/blink/trunk@184348 bbb929c8-8fbe-4397-9dbb-9b2b20218538