Implement Feature-Policy: lazyload

This CL implements the 'lazyload' policy which acts in place of the
lazyload attribute for nested frames and enforces lazyloading regardless
of the value of 'lazyload' attribute.

A follow up CL will implement the feature for images (after
LazyImageLoading is implemented).

Bug: 869492
Change-Id: I2f8ab7ad9a5937636f270c84563c73ad392dbb01
Reviewed-on: https://chromium-review.googlesource.com/1171374
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Reviewed-by: Scott Little <sclittle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590688}
15 files changed