Move PreviousBoxGeometries from BoxPaintInvalidator into LayoutBox::m_rareData

After https://codereview.chromium.org/2689213013/ and
https://codereview.chromium.org/2701103003/, now only 0.36% of
LayoutBoxes need PreviousBoxGeometries. Move it into
LayoutBox::m_rareData to simplify code and avoid map accesses.

BUG=685179
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2707073002
Cr-Commit-Position: refs/heads/master@{#452337}
5 files changed