Update layout tests to work when smooth scrolling is enabled by default

This CL updates expectations for tests that expect an instant scroll such
that they pass when smooth scroll is enabled.

Note:
- Some of the tests are re-written, but most of them apply the following change:
  shouldBe('scrollLeft', 'expectedScrollLeft)
  shouldBe('scrollTop', 'expectedScrollTop') -->
  shouldBecomeEqual('scrollLeft == expectedScrollLeft && scrollTop ==
    expectedScrollTop', 'true')
'shouldBecomeEqual' waits asynchronously until the condition is true.
- Some of the tests just expect a certain scroll offset and are not really
testing scroll-behavior. For those tests, the scrollAnimatorEnabled setting
is turned off by default.
  internals.settings.setScrollAnimatorEnabled(false)

BUG=575

Review URL: https://codereview.chromium.org/1413493005

Cr-Commit-Position: refs/heads/master@{#358572}
66 files changed