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This CL creates a bool in WebSettings to enable lazyloading of frames and images.
The bool is populated by WebContentsDelegate which offline pages listens to and
disables lazy loading.

Bug: 701884
Change-Id: I1ad1776adf3f9c7e6a8a3a68507aa9dc419e3955
Reviewed-on: https://chromium-review.googlesource.com/c/1352817
Commit-Queue: rajendrant <rajendrant@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Peter Williamson <petewil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612507}