Apply 'lazyload' feature policy for images

In CL 1171374 'lazyload' feature policy was introduced as a new
policy-controlled feature which would modify (restrict) the usage of the
lazyload attribute. The implementation only applied the feature to frame
owner elements. This CL extends the policy's coverage to images as well.

Bug: 869492
Change-Id: I9a2bd309ac366b75308b657d3ea129a7717ad23f
Reviewed-on: https://chromium-review.googlesource.com/c/1251024
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Reviewed-by: rajendrant <rajendrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599204}
12 files changed