Fix caret paint invalidation issues

Fix caret paint invalidation issues

- We should save CaretDisplayItemClient::m_previousLayoutBlock only if
  it has not been saved since the last paint invalidation, because we
  use it to invalidate the caret in the layout block of the previous
  paint invalidation.

- Caret painted output can change paint offset without visual rect
  change. Invalidate display item client if the block is doing full
  paint invalidation.

BUG=699044, 698662
TBR=wangxianzhu@chromium.org
NOTRY=true
NOPRESUBMIT=true
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2736213002
Cr-Commit-Position: refs/heads/master@{#455657}

[Xianzhu, 2017-03-10 17:04:10]

The CQ bit was checked by wangxianzhu@chromium.org

[commit-bot: I haz the power, 2017-03-10 17:04:38]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-03-10 17:05:56]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1489165450439840, "parent_rev":
"8aa2597c18b4dc96ca1fd2ab3311e7ce1084194c", "commit_rev":
"d414296eea8296839c18ba2d4e2b703735526373"}

[commit-bot: I haz the power, 2017-03-10 17:08:24]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-03-10 17:08:24]

Prior attempt to commit was detected, but we were not able to check whether the
issue was successfully committed. Please check Git history manually and re-check
CQ or close this issue as needed.