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- If PrepareToDraw indicates a scene change, do layout.
- Trigger scene rendering if the cursor moved.
- Move a static assert to live with TextInputInfo.
- Add more tests.

BUG=
R=mthiesse, ymalik

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I4f05832610c0d8e0676599bc92b9a926afbbca57
Reviewed-on: https://chromium-review.googlesource.com/809827
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Reviewed-by: Yash Malik <ymalik@chromium.org>
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522249}