Move tolerance from per color rect expectation to per page

First, we never have different tolerance values within the same page.

Second, moving tolerance to page allows us to reuse many of the
color expectations.

This is a follow-up for
https://chromium-review.googlesource.com/c/chromium/src/+/1457429

BUG=927901
TEST=pixel tests, maps_tests on GPU bots
R=kbr@chromium.org

Change-Id: Ib2866dd19bd684b69cc1df3c4721b0cb4a0b118b
Reviewed-on: https://chromium-review.googlesource.com/c/1468064
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Zhenyao Mo <zmo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631453}